diff options
Diffstat (limited to 'drivers/lguest/page_tables.c')
| -rw-r--r-- | drivers/lguest/page_tables.c | 1239 |
1 files changed, 0 insertions, 1239 deletions
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c deleted file mode 100644 index 0bc127e9f16a..000000000000 --- a/drivers/lguest/page_tables.c +++ /dev/null @@ -1,1239 +0,0 @@ -/*P:700 - * The pagetable code, on the other hand, still shows the scars of - * previous encounters. It's functional, and as neat as it can be in the - * circumstances, but be wary, for these things are subtle and break easily. - * The Guest provides a virtual to physical mapping, but we can neither trust - * it nor use it: we verify and convert it here then point the CPU to the - * converted Guest pages when running the Guest. -:*/ - -/* Copyright (C) Rusty Russell IBM Corporation 2013. - * GPL v2 and any later version */ -#include <linux/mm.h> -#include <linux/gfp.h> -#include <linux/types.h> -#include <linux/spinlock.h> -#include <linux/random.h> -#include <linux/percpu.h> -#include <asm/tlbflush.h> -#include <linux/uaccess.h> -#include "lg.h" - -/*M:008 - * We hold reference to pages, which prevents them from being swapped. - * It'd be nice to have a callback in the "struct mm_struct" when Linux wants - * to swap out. If we had this, and a shrinker callback to trim PTE pages, we - * could probably consider launching Guests as non-root. -:*/ - -/*H:300 - * The Page Table Code - * - * We use two-level page tables for the Guest, or three-level with PAE. If - * you're not entirely comfortable with virtual addresses, physical addresses - * and page tables then I recommend you review arch/x86/lguest/boot.c's "Page - * Table Handling" (with diagrams!). - * - * The Guest keeps page tables, but we maintain the actual ones here: these are - * called "shadow" page tables. Which is a very Guest-centric name: these are - * the real page tables the CPU uses, although we keep them up to date to - * reflect the Guest's. (See what I mean about weird naming? Since when do - * shadows reflect anything?) - * - * Anyway, this is the most complicated part of the Host code. There are seven - * parts to this: - * (i) Looking up a page table entry when the Guest faults, - * (ii) Making sure the Guest stack is mapped, - * (iii) Setting up a page table entry when the Guest tells us one has changed, - * (iv) Switching page tables, - * (v) Flushing (throwing away) page tables, - * (vi) Mapping the Switcher when the Guest is about to run, - * (vii) Setting up the page tables initially. -:*/ - -/* - * The Switcher uses the complete top PTE page. That's 1024 PTE entries (4MB) - * or 512 PTE entries with PAE (2MB). - */ -#define SWITCHER_PGD_INDEX (PTRS_PER_PGD - 1) - -/* - * For PAE we need the PMD index as well. We use the last 2MB, so we - * will need the last pmd entry of the last pmd page. - */ -#ifdef CONFIG_X86_PAE -#define CHECK_GPGD_MASK _PAGE_PRESENT -#else -#define CHECK_GPGD_MASK _PAGE_TABLE -#endif - -/*H:320 - * The page table code is curly enough to need helper functions to keep it - * clear and clean. The kernel itself provides many of them; one advantage - * of insisting that the Guest and Host use the same CONFIG_X86_PAE setting. - * - * There are two functions which return pointers to the shadow (aka "real") - * page tables. - * - * spgd_addr() takes the virtual address and returns a pointer to the top-level - * page directory entry (PGD) for that address. Since we keep track of several - * page tables, the "i" argument tells us which one we're interested in (it's - * usually the current one). - */ -static pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr) -{ - unsigned int index = pgd_index(vaddr); - - /* Return a pointer index'th pgd entry for the i'th page table. */ - return &cpu->lg->pgdirs[i].pgdir[index]; -} - -#ifdef CONFIG_X86_PAE -/* - * This routine then takes the PGD entry given above, which contains the - * address of the PMD page. It then returns a pointer to the PMD entry for the - * given address. - */ -static pmd_t *spmd_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr) -{ - unsigned int index = pmd_index(vaddr); - pmd_t *page; - - /* You should never call this if the PGD entry wasn't valid */ - BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT)); - page = __va(pgd_pfn(spgd) << PAGE_SHIFT); - - return &page[index]; -} -#endif - -/* - * This routine then takes the page directory entry returned above, which - * contains the address of the page table entry (PTE) page. It then returns a - * pointer to the PTE entry for the given address. - */ -static pte_t *spte_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr) -{ -#ifdef CONFIG_X86_PAE - pmd_t *pmd = spmd_addr(cpu, spgd, vaddr); - pte_t *page = __va(pmd_pfn(*pmd) << PAGE_SHIFT); - - /* You should never call this if the PMD entry wasn't valid */ - BUG_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT)); -#else - pte_t *page = __va(pgd_pfn(spgd) << PAGE_SHIFT); - /* You should never call this if the PGD entry wasn't valid */ - BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT)); -#endif - - return &page[pte_index(vaddr)]; -} - -/* - * These functions are just like the above, except they access the Guest - * page tables. Hence they return a Guest address. - */ -static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr) -{ - unsigned int index = vaddr >> (PGDIR_SHIFT); - return cpu->lg->pgdirs[cpu->cpu_pgd].gpgdir + index * sizeof(pgd_t); -} - -#ifdef CONFIG_X86_PAE -/* Follow the PGD to the PMD. */ -static unsigned long gpmd_addr(pgd_t gpgd, unsigned long vaddr) -{ - unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT; - BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT)); - return gpage + pmd_index(vaddr) * sizeof(pmd_t); -} - -/* Follow the PMD to the PTE. */ -static unsigned long gpte_addr(struct lg_cpu *cpu, - pmd_t gpmd, unsigned long vaddr) -{ - unsigned long gpage = pmd_pfn(gpmd) << PAGE_SHIFT; - - BUG_ON(!(pmd_flags(gpmd) & _PAGE_PRESENT)); - return gpage + pte_index(vaddr) * sizeof(pte_t); -} -#else -/* Follow the PGD to the PTE (no mid-level for !PAE). */ -static unsigned long gpte_addr(struct lg_cpu *cpu, - pgd_t gpgd, unsigned long vaddr) -{ - unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT; - - BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT)); - return gpage + pte_index(vaddr) * sizeof(pte_t); -} -#endif -/*:*/ - -/*M:007 - * get_pfn is slow: we could probably try to grab batches of pages here as - * an optimization (ie. pre-faulting). -:*/ - -/*H:350 - * This routine takes a page number given by the Guest and converts it to - * an actual, physical page number. It can fail for several reasons: the - * virtual address might not be mapped by the Launcher, the write flag is set - * and the page is read-only, or the write flag was set and the page was - * shared so had to be copied, but we ran out of memory. - * - * This holds a reference to the page, so release_pte() is careful to put that - * back. - */ -static unsigned long get_pfn(unsigned long virtpfn, int write) -{ - struct page *page; - - /* gup me one page at this address please! */ - if (get_user_pages_fast(virtpfn << PAGE_SHIFT, 1, write, &page) == 1) - return page_to_pfn(page); - - /* This value indicates failure. */ - return -1UL; -} - -/*H:340 - * Converting a Guest page table entry to a shadow (ie. real) page table - * entry can be a little tricky. The flags are (almost) the same, but the - * Guest PTE contains a virtual page number: the CPU needs the real page - * number. - */ -static pte_t gpte_to_spte(struct lg_cpu *cpu, pte_t gpte, int write) -{ - unsigned long pfn, base, flags; - - /* - * The Guest sets the global flag, because it thinks that it is using - * PGE. We only told it to use PGE so it would tell us whether it was - * flushing a kernel mapping or a userspace mapping. We don't actually - * use the global bit, so throw it away. - */ - flags = (pte_flags(gpte) & ~_PAGE_GLOBAL); - - /* The Guest's pages are offset inside the Launcher. */ - base = (unsigned long)cpu->lg->mem_base / PAGE_SIZE; - - /* - * We need a temporary "unsigned long" variable to hold the answer from - * get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't - * fit in spte.pfn. get_pfn() finds the real physical number of the - * page, given the virtual number. - */ - pfn = get_pfn(base + pte_pfn(gpte), write); - if (pfn == -1UL) { - kill_guest(cpu, "failed to get page %lu", pte_pfn(gpte)); - /* - * When we destroy the Guest, we'll go through the shadow page - * tables and release_pte() them. Make sure we don't think - * this one is valid! - */ - flags = 0; - } - /* Now we assemble our shadow PTE from the page number and flags. */ - return pfn_pte(pfn, __pgprot(flags)); -} - -/*H:460 And to complete the chain, release_pte() looks like this: */ -static void release_pte(pte_t pte) -{ - /* - * Remember that get_user_pages_fast() took a reference to the page, in - * get_pfn()? We have to put it back now. - */ - if (pte_flags(pte) & _PAGE_PRESENT) - put_page(pte_page(pte)); -} -/*:*/ - -static bool gpte_in_iomem(struct lg_cpu *cpu, pte_t gpte) -{ - /* We don't handle large pages. */ - if (pte_flags(gpte) & _PAGE_PSE) - return false; - - return (pte_pfn(gpte) >= cpu->lg->pfn_limit - && pte_pfn(gpte) < cpu->lg->device_limit); -} - -static bool check_gpte(struct lg_cpu *cpu, pte_t gpte) -{ - if ((pte_flags(gpte) & _PAGE_PSE) || - pte_pfn(gpte) >= cpu->lg->pfn_limit) { - kill_guest(cpu, "bad page table entry"); - return false; - } - return true; -} - -static bool check_gpgd(struct lg_cpu *cpu, pgd_t gpgd) -{ - if ((pgd_flags(gpgd) & ~CHECK_GPGD_MASK) || - (pgd_pfn(gpgd) >= cpu->lg->pfn_limit)) { - kill_guest(cpu, "bad page directory entry"); - return false; - } - return true; -} - -#ifdef CONFIG_X86_PAE -static bool check_gpmd(struct lg_cpu *cpu, pmd_t gpmd) -{ - if ((pmd_flags(gpmd) & ~_PAGE_TABLE) || - (pmd_pfn(gpmd) >= cpu->lg->pfn_limit)) { - kill_guest(cpu, "bad page middle directory entry"); - return false; - } - return true; -} -#endif - -/*H:331 - * This is the core routine to walk the shadow page tables and find the page - * table entry for a specific address. - * - * If allocate is set, then we allocate any missing levels, setting the flags - * on the new page directory and mid-level directories using the arguments - * (which are copied from the Guest's page table entries). - */ -static pte_t *find_spte(struct lg_cpu *cpu, unsigned long vaddr, bool allocate, - int pgd_flags, int pmd_flags) -{ - pgd_t *spgd; - /* Mid level for PAE. */ -#ifdef CONFIG_X86_PAE - pmd_t *spmd; -#endif - - /* Get top level entry. */ - spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr); - if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) { - /* No shadow entry: allocate a new shadow PTE page. */ - unsigned long ptepage; - - /* If they didn't want us to allocate anything, stop. */ - if (!allocate) - return NULL; - - ptepage = get_zeroed_page(GFP_KERNEL); - /* - * This is not really the Guest's fault, but killing it is - * simple for this corner case. - */ - if (!ptepage) { - kill_guest(cpu, "out of memory allocating pte page"); - return NULL; - } - /* - * And we copy the flags to the shadow PGD entry. The page - * number in the shadow PGD is the page we just allocated. - */ - set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags)); - } - - /* - * Intel's Physical Address Extension actually uses three levels of - * page tables, so we need to look in the mid-level. - */ -#ifdef CONFIG_X86_PAE - /* Now look at the mid-level shadow entry. */ - spmd = spmd_addr(cpu, *spgd, vaddr); - - if (!(pmd_flags(*spmd) & _PAGE_PRESENT)) { - /* No shadow entry: allocate a new shadow PTE page. */ - unsigned long ptepage; - - /* If they didn't want us to allocate anything, stop. */ - if (!allocate) - return NULL; - - ptepage = get_zeroed_page(GFP_KERNEL); - - /* - * This is not really the Guest's fault, but killing it is - * simple for this corner case. - */ - if (!ptepage) { - kill_guest(cpu, "out of memory allocating pmd page"); - return NULL; - } - - /* - * And we copy the flags to the shadow PMD entry. The page - * number in the shadow PMD is the page we just allocated. - */ - set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags)); - } -#endif - - /* Get the pointer to the shadow PTE entry we're going to set. */ - return spte_addr(cpu, *spgd, vaddr); -} - -/*H:330 - * (i) Looking up a page table entry when the Guest faults. - * - * We saw this call in run_guest(): when we see a page fault in the Guest, we - * come here. That's because we only set up the shadow page tables lazily as - * they're needed, so we get page faults all the time and quietly fix them up - * and return to the Guest without it knowing. - * - * If we fixed up the fault (ie. we mapped the address), this routine returns - * true. Otherwise, it was a real fault and we need to tell the Guest. - * - * There's a corner case: they're trying to access memory between - * pfn_limit and device_limit, which is I/O memory. In this case, we - * return false and set @iomem to the physical address, so the the - * Launcher can handle the instruction manually. - */ -bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode, - unsigned long *iomem) -{ - unsigned long gpte_ptr; - pte_t gpte; - pte_t *spte; - pmd_t gpmd; - pgd_t gpgd; - - *iomem = 0; - - /* We never demand page the Switcher, so trying is a mistake. */ - if (vaddr >= switcher_addr) - return false; - - /* First step: get the top-level Guest page table entry. */ - if (unlikely(cpu->linear_pages)) { - /* Faking up a linear mapping. */ - gpgd = __pgd(CHECK_GPGD_MASK); - } else { - gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t); - /* Toplevel not present? We can't map it in. */ - if (!(pgd_flags(gpgd) & _PAGE_PRESENT)) - return false; - - /* - * This kills the Guest if it has weird flags or tries to - * refer to a "physical" address outside the bounds. - */ - if (!check_gpgd(cpu, gpgd)) - return false; - } - - /* This "mid-level" entry is only used for non-linear, PAE mode. */ - gpmd = __pmd(_PAGE_TABLE); - -#ifdef CONFIG_X86_PAE - if (likely(!cpu->linear_pages)) { - gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t); - /* Middle level not present? We can't map it in. */ - if (!(pmd_flags(gpmd) & _PAGE_PRESENT)) - return false; - - /* - * This kills the Guest if it has weird flags or tries to - * refer to a "physical" address outside the bounds. - */ - if (!check_gpmd(cpu, gpmd)) - return false; - } - - /* - * OK, now we look at the lower level in the Guest page table: keep its - * address, because we might update it later. - */ - gpte_ptr = gpte_addr(cpu, gpmd, vaddr); -#else - /* - * OK, now we look at the lower level in the Guest page table: keep its - * address, because we might update it later. - */ - gpte_ptr = gpte_addr(cpu, gpgd, vaddr); -#endif - - if (unlikely(cpu->linear_pages)) { - /* Linear? Make up a PTE which points to same page. */ - gpte = __pte((vaddr & PAGE_MASK) | _PAGE_RW | _PAGE_PRESENT); - } else { - /* Read the actual PTE value. */ - gpte = lgread(cpu, gpte_ptr, pte_t); - } - - /* If this page isn't in the Guest page tables, we can't page it in. */ - if (!(pte_flags(gpte) & _PAGE_PRESENT)) - return false; - - /* - * Check they're not trying to write to a page the Guest wants - * read-only (bit 2 of errcode == write). - */ - if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW)) - return false; - - /* User access to a kernel-only page? (bit 3 == user access) */ - if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER)) - return false; - - /* If they're accessing io memory, we expect a fault. */ - if (gpte_in_iomem(cpu, gpte)) { - *iomem = (pte_pfn(gpte) << PAGE_SHIFT) | (vaddr & ~PAGE_MASK); - return false; - } - - /* - * Check that the Guest PTE flags are OK, and the page number is below - * the pfn_limit (ie. not mapping the Launcher binary). - */ - if (!check_gpte(cpu, gpte)) - return false; - - /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */ - gpte = pte_mkyoung(gpte); - if (errcode & 2) - gpte = pte_mkdirty(gpte); - - /* Get the pointer to the shadow PTE entry we're going to set. */ - spte = find_spte(cpu, vaddr, true, pgd_flags(gpgd), pmd_flags(gpmd)); - if (!spte) - return false; - - /* - * If there was a valid shadow PTE entry here before, we release it. - * This can happen with a write to a previously read-only entry. - */ - release_pte(*spte); - - /* - * If this is a write, we insist that the Guest page is writable (the - * final arg to gpte_to_spte()). - */ - if (pte_dirty(gpte)) - *spte = gpte_to_spte(cpu, gpte, 1); - else - /* - * If this is a read, don't set the "writable" bit in the page - * table entry, even if the Guest says it's writable. That way - * we will come back here when a write does actually occur, so - * we can update the Guest's _PAGE_DIRTY flag. - */ - set_pte(spte, gpte_to_spte(cpu, pte_wrprotect(gpte), 0)); - - /* - * Finally, we write the Guest PTE entry back: we've set the - * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags. - */ - if (likely(!cpu->linear_pages)) - lgwrite(cpu, gpte_ptr, pte_t, gpte); - - /* - * The fault is fixed, the page table is populated, the mapping - * manipulated, the result returned and the code complete. A small - * delay and a trace of alliteration are the only indications the Guest - * has that a page fault occurred at all. - */ - return true; -} - -/*H:360 - * (ii) Making sure the Guest stack is mapped. - * - * Remember that direct traps into the Guest need a mapped Guest kernel stack. - * pin_stack_pages() calls us here: we could simply call demand_page(), but as - * we've seen that logic is quite long, and usually the stack pages are already - * mapped, so it's overkill. - * - * This is a quick version which answers the question: is this virtual address - * mapped by the shadow page tables, and is it writable? - */ -static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr) -{ - pte_t *spte; - unsigned long flags; - - /* You can't put your stack in the Switcher! */ - if (vaddr >= switcher_addr) - return false; - - /* If there's no shadow PTE, it's not writable. */ - spte = find_spte(cpu, vaddr, false, 0, 0); - if (!spte) - return false; - - /* - * Check the flags on the pte entry itself: it must be present and - * writable. - */ - flags = pte_flags(*spte); - return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW); -} - -/* - * So, when pin_stack_pages() asks us to pin a page, we check if it's already - * in the page tables, and if not, we call demand_page() with error code 2 - * (meaning "write"). - */ -void pin_page(struct lg_cpu *cpu, unsigned long vaddr) -{ - unsigned long iomem; - - if (!page_writable(cpu, vaddr) && !demand_page(cpu, vaddr, 2, &iomem)) - kill_guest(cpu, "bad stack page %#lx", vaddr); -} -/*:*/ - -#ifdef CONFIG_X86_PAE -static void release_pmd(pmd_t *spmd) -{ - /* If the entry's not present, there's nothing to release. */ - if (pmd_flags(*spmd) & _PAGE_PRESENT) { - unsigned int i; - pte_t *ptepage = __va(pmd_pfn(*spmd) << PAGE_SHIFT); - /* For each entry in the page, we might need to release it. */ - for (i = 0; i < PTRS_PER_PTE; i++) - release_pte(ptepage[i]); - /* Now we can free the page of PTEs */ - free_page((long)ptepage); - /* And zero out the PMD entry so we never release it twice. */ - set_pmd(spmd, __pmd(0)); - } -} - -static void release_pgd(pgd_t *spgd) -{ - /* If the entry's not present, there's nothing to release. */ - if (pgd_flags(*spgd) & _PAGE_PRESENT) { - unsigned int i; - pmd_t *pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT); - - for (i = 0; i < PTRS_PER_PMD; i++) - release_pmd(&pmdpage[i]); - - /* Now we can free the page of PMDs */ - free_page((long)pmdpage); - /* And zero out the PGD entry so we never release it twice. */ - set_pgd(spgd, __pgd(0)); - } -} - -#else /* !CONFIG_X86_PAE */ -/*H:450 - * If we chase down the release_pgd() code, the non-PAE version looks like - * this. The PAE version is almost identical, but instead of calling - * release_pte it calls release_pmd(), which looks much like this. - */ -static void release_pgd(pgd_t *spgd) -{ - /* If the entry's not present, there's nothing to release. */ - if (pgd_flags(*spgd) & _PAGE_PRESENT) { - unsigned int i; - /* - * Converting the pfn to find the actual PTE page is easy: turn - * the page number into a physical address, then convert to a - * virtual address (easy for kernel pages like this one). - */ - pte_t *ptepage = __va(pgd_pfn(*spgd) << PAGE_SHIFT); - /* For each entry in the page, we might need to release it. */ - for (i = 0; i < PTRS_PER_PTE; i++) - release_pte(ptepage[i]); - /* Now we can free the page of PTEs */ - free_page((long)ptepage); - /* And zero out the PGD entry so we never release it twice. */ - *spgd = __pgd(0); - } -} -#endif - -/*H:445 - * We saw flush_user_mappings() twice: once from the flush_user_mappings() - * hypercall and once in new_pgdir() when we re-used a top-level pgdir page. - * It simply releases every PTE page from 0 up to the Guest's kernel address. - */ -static void flush_user_mappings(struct lguest *lg, int idx) -{ - unsigned int i; - /* Release every pgd entry up to the kernel's address. */ - for (i = 0; i < pgd_index(lg->kernel_address); i++) - release_pgd(lg->pgdirs[idx].pgdir + i); -} - -/*H:440 - * (v) Flushing (throwing away) page tables, - * - * The Guest has a hypercall to throw away the page tables: it's used when a - * large number of mappings have been changed. - */ -void guest_pagetable_flush_user(struct lg_cpu *cpu) -{ - /* Drop the userspace part of the current page table. */ - flush_user_mappings(cpu->lg, cpu->cpu_pgd); -} -/*:*/ - -/* We walk down the guest page tables to get a guest-physical address */ -bool __guest_pa(struct lg_cpu *cpu, unsigned long vaddr, unsigned long *paddr) -{ - pgd_t gpgd; - pte_t gpte; -#ifdef CONFIG_X86_PAE - pmd_t gpmd; -#endif - - /* Still not set up? Just map 1:1. */ - if (unlikely(cpu->linear_pages)) { - *paddr = vaddr; - return true; - } - - /* First step: get the top-level Guest page table entry. */ - gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t); - /* Toplevel not present? We can't map it in. */ - if (!(pgd_flags(gpgd) & _PAGE_PRESENT)) - goto fail; - -#ifdef CONFIG_X86_PAE - gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t); - if (!(pmd_flags(gpmd) & _PAGE_PRESENT)) - goto fail; - gpte = lgread(cpu, gpte_addr(cpu, gpmd, vaddr), pte_t); -#else - gpte = lgread(cpu, gpte_addr(cpu, gpgd, vaddr), pte_t); -#endif - if (!(pte_flags(gpte) & _PAGE_PRESENT)) - goto fail; - - *paddr = pte_pfn(gpte) * PAGE_SIZE | (vaddr & ~PAGE_MASK); - return true; - -fail: - *paddr = -1UL; - return false; -} - -/* - * This is the version we normally use: kills the Guest if it uses a - * bad address - */ -unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr) -{ - unsigned long paddr; - - if (!__guest_pa(cpu, vaddr, &paddr)) - kill_guest(cpu, "Bad address %#lx", vaddr); - return paddr; -} - -/* - * We keep several page tables. This is a simple routine to find the page - * table (if any) corresponding to this top-level address the Guest has given - * us. - */ -static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable) -{ - unsigned int i; - for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) - if (lg->pgdirs[i].pgdir && lg->pgdirs[i].gpgdir == pgtable) - break; - return i; -} - -/*H:435 - * And this is us, creating the new page directory. If we really do - * allocate a new one (and so the kernel parts are not there), we set - * blank_pgdir. - */ -static unsigned int new_pgdir(struct lg_cpu *cpu, - unsigned long gpgdir, - int *blank_pgdir) -{ - unsigned int next; - - /* - * We pick one entry at random to throw out. Choosing the Least - * Recently Used might be better, but this is easy. - */ - next = prandom_u32() % ARRAY_SIZE(cpu->lg->pgdirs); - /* If it's never been allocated at all before, try now. */ - if (!cpu->lg->pgdirs[next].pgdir) { - cpu->lg->pgdirs[next].pgdir = - (pgd_t *)get_zeroed_page(GFP_KERNEL); - /* If the allocation fails, just keep using the one we have */ - if (!cpu->lg->pgdirs[next].pgdir) - next = cpu->cpu_pgd; - else { - /* - * This is a blank page, so there are no kernel - * mappings: caller must map the stack! - */ - *blank_pgdir = 1; - } - } - /* Record which Guest toplevel this shadows. */ - cpu->lg->pgdirs[next].gpgdir = gpgdir; - /* Release all the non-kernel mappings. */ - flush_user_mappings(cpu->lg, next); - - /* This hasn't run on any CPU at all. */ - cpu->lg->pgdirs[next].last_host_cpu = -1; - - return next; -} - -/*H:501 - * We do need the Switcher code mapped at all times, so we allocate that - * part of the Guest page table here. We map the Switcher code immediately, - * but defer mapping of the guest register page and IDT/LDT etc page until - * just before we run the guest in map_switcher_in_guest(). - * - * We *could* do this setup in map_switcher_in_guest(), but at that point - * we've interrupts disabled, and allocating pages like that is fraught: we - * can't sleep if we need to free up some memory. - */ -static bool allocate_switcher_mapping(struct lg_cpu *cpu) -{ - int i; - - for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) { - pte_t *pte = find_spte(cpu, switcher_addr + i * PAGE_SIZE, true, - CHECK_GPGD_MASK, _PAGE_TABLE); - if (!pte) - return false; - - /* - * Map the switcher page if not already there. It might - * already be there because we call allocate_switcher_mapping() - * in guest_set_pgd() just in case it did discard our Switcher - * mapping, but it probably didn't. - */ - if (i == 0 && !(pte_flags(*pte) & _PAGE_PRESENT)) { - /* Get a reference to the Switcher page. */ - get_page(lg_switcher_pages[0]); - /* Create a read-only, exectuable, kernel-style PTE */ - set_pte(pte, - mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX)); - } - } - cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped = true; - return true; -} - -/*H:470 - * Finally, a routine which throws away everything: all PGD entries in all - * the shadow page tables, including the Guest's kernel mappings. This is used - * when we destroy the Guest. - */ -static void release_all_pagetables(struct lguest *lg) -{ - unsigned int i, j; - - /* Every shadow pagetable this Guest has */ - for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) { - if (!lg->pgdirs[i].pgdir) - continue; - - /* Every PGD entry. */ - for (j = 0; j < PTRS_PER_PGD; j++) - release_pgd(lg->pgdirs[i].pgdir + j); - lg->pgdirs[i].switcher_mapped = false; - lg->pgdirs[i].last_host_cpu = -1; - } -} - -/* - * We also throw away everything when a Guest tells us it's changed a kernel - * mapping. Since kernel mappings are in every page table, it's easiest to - * throw them all away. This traps the Guest in amber for a while as - * everything faults back in, but it's rare. - */ -void guest_pagetable_clear_all(struct lg_cpu *cpu) -{ - release_all_pagetables(cpu->lg); - /* We need the Guest kernel stack mapped again. */ - pin_stack_pages(cpu); - /* And we need Switcher allocated. */ - if (!allocate_switcher_mapping(cpu)) - kill_guest(cpu, "Cannot populate switcher mapping"); -} - -/*H:430 - * (iv) Switching page tables - * - * Now we've seen all the page table setting and manipulation, let's see - * what happens when the Guest changes page tables (ie. changes the top-level - * pgdir). This occurs on almost every context switch. - */ -void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable) -{ - int newpgdir, repin = 0; - - /* - * The very first time they call this, we're actually running without - * any page tables; we've been making it up. Throw them away now. - */ - if (unlikely(cpu->linear_pages)) { - release_all_pagetables(cpu->lg); - cpu->linear_pages = false; - /* Force allocation of a new pgdir. */ - newpgdir = ARRAY_SIZE(cpu->lg->pgdirs); - } else { - /* Look to see if we have this one already. */ - newpgdir = find_pgdir(cpu->lg, pgtable); - } - - /* - * If not, we allocate or mug an existing one: if it's a fresh one, - * repin gets set to 1. - */ - if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs)) - newpgdir = new_pgdir(cpu, pgtable, &repin); - /* Change the current pgd index to the new one. */ - cpu->cpu_pgd = newpgdir; - /* - * If it was completely blank, we map in the Guest kernel stack and - * the Switcher. - */ - if (repin) - pin_stack_pages(cpu); - - if (!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped) { - if (!allocate_switcher_mapping(cpu)) - kill_guest(cpu, "Cannot populate switcher mapping"); - } -} -/*:*/ - -/*M:009 - * Since we throw away all mappings when a kernel mapping changes, our - * performance sucks for guests using highmem. In fact, a guest with - * PAGE_OFFSET 0xc0000000 (the default) and more than about 700MB of RAM is - * usually slower than a Guest with less memory. - * - * This, of course, cannot be fixed. It would take some kind of... well, I - * don't know, but the term "puissant code-fu" comes to mind. -:*/ - -/*H:420 - * This is the routine which actually sets the page table entry for then - * "idx"'th shadow page table. - * - * Normally, we can just throw out the old entry and replace it with 0: if they - * use it demand_page() will put the new entry in. We need to do this anyway: - * The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page - * is read from, and _PAGE_DIRTY when it's written to. - * - * But Avi Kivity pointed out that most Operating Systems (Linux included) set - * these bits on PTEs immediately anyway. This is done to save the CPU from - * having to update them, but it helps us the same way: if they set - * _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if - * they set _PAGE_DIRTY then we can put a writable PTE entry in immediately. - */ -static void __guest_set_pte(struct lg_cpu *cpu, int idx, - unsigned long vaddr, pte_t gpte) -{ - /* Look up the matching shadow page directory entry. */ - pgd_t *spgd = spgd_addr(cpu, idx, vaddr); -#ifdef CONFIG_X86_PAE - pmd_t *spmd; -#endif - - /* If the top level isn't present, there's no entry to update. */ - if (pgd_flags(*spgd) & _PAGE_PRESENT) { -#ifdef CONFIG_X86_PAE - spmd = spmd_addr(cpu, *spgd, vaddr); - if (pmd_flags(*spmd) & _PAGE_PRESENT) { -#endif - /* Otherwise, start by releasing the existing entry. */ - pte_t *spte = spte_addr(cpu, *spgd, vaddr); - release_pte(*spte); - - /* - * If they're setting this entry as dirty or accessed, - * we might as well put that entry they've given us in - * now. This shaves 10% off a copy-on-write - * micro-benchmark. - */ - if ((pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED)) - && !gpte_in_iomem(cpu, gpte)) { - if (!check_gpte(cpu, gpte)) - return; - set_pte(spte, - gpte_to_spte(cpu, gpte, - pte_flags(gpte) & _PAGE_DIRTY)); - } else { - /* - * Otherwise kill it and we can demand_page() - * it in later. - */ - set_pte(spte, __pte(0)); - } -#ifdef CONFIG_X86_PAE - } -#endif - } -} - -/*H:410 - * Updating a PTE entry is a little trickier. - * - * We keep track of several different page tables (the Guest uses one for each - * process, so it makes sense to cache at least a few). Each of these have - * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for - * all processes. So when the page table above that address changes, we update - * all the page tables, not just the current one. This is rare. - * - * The benefit is that when we have to track a new page table, we can keep all - * the kernel mappings. This speeds up context switch immensely. - */ -void guest_set_pte(struct lg_cpu *cpu, - unsigned long gpgdir, unsigned long vaddr, pte_t gpte) -{ - /* We don't let you remap the Switcher; we need it to get back! */ - if (vaddr >= switcher_addr) { - kill_guest(cpu, "attempt to set pte into Switcher pages"); - return; - } - - /* - * Kernel mappings must be changed on all top levels. Slow, but doesn't - * happen often. - */ - if (vaddr >= cpu->lg->kernel_address) { - unsigned int i; - for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++) - if (cpu->lg->pgdirs[i].pgdir) - __guest_set_pte(cpu, i, vaddr, gpte); - } else { - /* Is this page table one we have a shadow for? */ - int pgdir = find_pgdir(cpu->lg, gpgdir); - if (pgdir != ARRAY_SIZE(cpu->lg->pgdirs)) - /* If so, do the update. */ - __guest_set_pte(cpu, pgdir, vaddr, gpte); - } -} - -/*H:400 - * (iii) Setting up a page table entry when the Guest tells us one has changed. - * - * Just like we did in interrupts_and_traps.c, it makes sense for us to deal - * with the other side of page tables while we're here: what happens when the - * Guest asks for a page table to be updated? - * - * We already saw that demand_page() will fill in the shadow page tables when - * needed, so we can simply remove shadow page table entries whenever the Guest - * tells us they've changed. When the Guest tries to use the new entry it will - * fault and demand_page() will fix it up. - * - * So with that in mind here's our code to update a (top-level) PGD entry: - */ -void guest_set_pgd(struct lguest *lg, unsigned long gpgdir, u32 idx) -{ - int pgdir; - - if (idx > PTRS_PER_PGD) { - kill_guest(&lg->cpus[0], "Attempt to set pgd %u/%u", - idx, PTRS_PER_PGD); - return; - } - - /* If they're talking about a page table we have a shadow for... */ - pgdir = find_pgdir(lg, gpgdir); - if (pgdir < ARRAY_SIZE(lg->pgdirs)) { - /* ... throw it away. */ - release_pgd(lg->pgdirs[pgdir].pgdir + idx); - /* That might have been the Switcher mapping, remap it. */ - if (!allocate_switcher_mapping(&lg->cpus[0])) { - kill_guest(&lg->cpus[0], - "Cannot populate switcher mapping"); - } - lg->pgdirs[pgdir].last_host_cpu = -1; - } -} - -#ifdef CONFIG_X86_PAE -/* For setting a mid-level, we just throw everything away. It's easy. */ -void guest_set_pmd(struct lguest *lg, unsigned long pmdp, u32 idx) -{ - guest_pagetable_clear_all(&lg->cpus[0]); -} -#endif - -/*H:500 - * (vii) Setting up the page tables initially. - * - * When a Guest is first created, set initialize a shadow page table which - * we will populate on future faults. The Guest doesn't have any actual - * pagetables yet, so we set linear_pages to tell demand_page() to fake it - * for the moment. - * - * We do need the Switcher to be mapped at all times, so we allocate that - * part of the Guest page table here. - */ -int init_guest_pagetable(struct lguest *lg) -{ - struct lg_cpu *cpu = &lg->cpus[0]; - int allocated = 0; - - /* lg (and lg->cpus[]) starts zeroed: this allocates a new pgdir */ - cpu->cpu_pgd = new_pgdir(cpu, 0, &allocated); - if (!allocated) - return -ENOMEM; - - /* We start with a linear mapping until the initialize. */ - cpu->linear_pages = true; - - /* Allocate the page tables for the Switcher. */ - if (!allocate_switcher_mapping(cpu)) { - release_all_pagetables(lg); - return -ENOMEM; - } - - return 0; -} - -/*H:508 When the Guest calls LHCALL_LGUEST_INIT we do more setup. */ -void page_table_guest_data_init(struct lg_cpu *cpu) -{ - /* - * We tell the Guest that it can't use the virtual addresses - * used by the Switcher. This trick is equivalent to 4GB - - * switcher_addr. - */ - u32 top = ~switcher_addr + 1; - - /* We get the kernel address: above this is all kernel memory. */ - if (get_user(cpu->lg->kernel_address, - &cpu->lg->lguest_data->kernel_address) - /* - * We tell the Guest that it can't use the top virtual - * addresses (used by the Switcher). - */ - || put_user(top, &cpu->lg->lguest_data->reserve_mem)) { - kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data); - return; - } - - /* - * In flush_user_mappings() we loop from 0 to - * "pgd_index(lg->kernel_address)". This assumes it won't hit the - * Switcher mappings, so check that now. - */ - if (cpu->lg->kernel_address >= switcher_addr) - kill_guest(cpu, "bad kernel address %#lx", - cpu->lg->kernel_address); -} - -/* When a Guest dies, our cleanup is fairly simple. */ -void free_guest_pagetable(struct lguest *lg) -{ - unsigned int i; - - /* Throw away all page table pages. */ - release_all_pagetables(lg); - /* Now free the top levels: free_page() can handle 0 just fine. */ - for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) - free_page((long)lg->pgdirs[i].pgdir); -} - -/*H:481 - * This clears the Switcher mappings for cpu #i. - */ -static void remove_switcher_percpu_map(struct lg_cpu *cpu, unsigned int i) -{ - unsigned long base = switcher_addr + PAGE_SIZE + i * PAGE_SIZE*2; - pte_t *pte; - - /* Clear the mappings for both pages. */ - pte = find_spte(cpu, base, false, 0, 0); - release_pte(*pte); - set_pte(pte, __pte(0)); - - pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0); - release_pte(*pte); - set_pte(pte, __pte(0)); -} - -/*H:480 - * (vi) Mapping the Switcher when the Guest is about to run. - * - * The Switcher and the two pages for this CPU need to be visible in the Guest - * (and not the pages for other CPUs). - * - * The pages for the pagetables have all been allocated before: we just need - * to make sure the actual PTEs are up-to-date for the CPU we're about to run - * on. - */ -void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages) -{ - unsigned long base; - struct page *percpu_switcher_page, *regs_page; - pte_t *pte; - struct pgdir *pgdir = &cpu->lg->pgdirs[cpu->cpu_pgd]; - - /* Switcher page should always be mapped by now! */ - BUG_ON(!pgdir->switcher_mapped); - - /* - * Remember that we have two pages for each Host CPU, so we can run a - * Guest on each CPU without them interfering. We need to make sure - * those pages are mapped correctly in the Guest, but since we usually - * run on the same CPU, we cache that, and only update the mappings - * when we move. - */ - if (pgdir->last_host_cpu == raw_smp_processor_id()) - return; - - /* -1 means unknown so we remove everything. */ - if (pgdir->last_host_cpu == -1) { - unsigned int i; - for_each_possible_cpu(i) - remove_switcher_percpu_map(cpu, i); - } else { - /* We know exactly what CPU mapping to remove. */ - remove_switcher_percpu_map(cpu, pgdir->last_host_cpu); - } - - /* - * When we're running the Guest, we want the Guest's "regs" page to - * appear where the first Switcher page for this CPU is. This is an - * optimization: when the Switcher saves the Guest registers, it saves - * them into the first page of this CPU's "struct lguest_pages": if we - * make sure the Guest's register page is already mapped there, we - * don't have to copy them out again. - */ - /* Find the shadow PTE for this regs page. */ - base = switcher_addr + PAGE_SIZE - + raw_smp_processor_id() * sizeof(struct lguest_pages); - pte = find_spte(cpu, base, false, 0, 0); - regs_page = pfn_to_page(__pa(cpu->regs_page) >> PAGE_SHIFT); - get_page(regs_page); - set_pte(pte, mk_pte(regs_page, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL))); - - /* - * We map the second page of the struct lguest_pages read-only in - * the Guest: the IDT, GDT and other things it's not supposed to - * change. - */ - pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0); - percpu_switcher_page - = lg_switcher_pages[1 + raw_smp_processor_id()*2 + 1]; - get_page(percpu_switcher_page); - set_pte(pte, mk_pte(percpu_switcher_page, - __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL))); - - pgdir->last_host_cpu = raw_smp_processor_id(); -} - -/*H:490 - * We've made it through the page table code. Perhaps our tired brains are - * still processing the details, or perhaps we're simply glad it's over. - * - * If nothing else, note that all this complexity in juggling shadow page tables - * in sync with the Guest's page tables is for one reason: for most Guests this - * page table dance determines how bad performance will be. This is why Xen - * uses exotic direct Guest pagetable manipulation, and why both Intel and AMD - * have implemented shadow page table support directly into hardware. - * - * There is just one file remaining in the Host. - */ |