diff options
Diffstat (limited to 'mm/memory.c')
| -rw-r--r-- | mm/memory.c | 99 |
1 files changed, 55 insertions, 44 deletions
diff --git a/mm/memory.c b/mm/memory.c index 0da414c383e7..c5e88bcd8ec3 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -371,33 +371,37 @@ static inline int is_cow_mapping(unsigned int flags) } /* - * This function gets the "struct page" associated with a pte or returns - * NULL if no "struct page" is associated with the pte. + * vm_normal_page -- This function gets the "struct page" associated with a pte. * - * A raw VM_PFNMAP mapping (ie. one that is not COWed) may not have any "struct - * page" backing, and even if they do, they are not refcounted. COWed pages of - * a VM_PFNMAP do always have a struct page, and they are normally refcounted - * (they are _normal_ pages). + * "Special" mappings do not wish to be associated with a "struct page" (either + * it doesn't exist, or it exists but they don't want to touch it). In this + * case, NULL is returned here. "Normal" mappings do have a struct page. * - * So a raw PFNMAP mapping will have each page table entry just pointing - * to a page frame number, and as far as the VM layer is concerned, those do - * not have pages associated with them - even if the PFN might point to memory - * that otherwise is perfectly fine and has a "struct page". + * There are 2 broad cases. Firstly, an architecture may define a pte_special() + * pte bit, in which case this function is trivial. Secondly, an architecture + * may not have a spare pte bit, which requires a more complicated scheme, + * described below. + * + * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a + * special mapping (even if there are underlying and valid "struct pages"). + * COWed pages of a VM_PFNMAP are always normal. * * The way we recognize COWed pages within VM_PFNMAP mappings is through the * rules set up by "remap_pfn_range()": the vma will have the VM_PFNMAP bit - * set, and the vm_pgoff will point to the first PFN mapped: thus every - * page that is a raw mapping will always honor the rule + * set, and the vm_pgoff will point to the first PFN mapped: thus every special + * mapping will always honor the rule * * pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT) * - * A call to vm_normal_page() will return NULL for such a page. + * And for normal mappings this is false. + * + * This restricts such mappings to be a linear translation from virtual address + * to pfn. To get around this restriction, we allow arbitrary mappings so long + * as the vma is not a COW mapping; in that case, we know that all ptes are + * special (because none can have been COWed). * - * If the page doesn't follow the "remap_pfn_range()" rule in a VM_PFNMAP - * then the page has been COW'ed. A COW'ed page _does_ have a "struct page" - * associated with it even if it is in a VM_PFNMAP range. Calling - * vm_normal_page() on such a page will therefore return the "struct page". * + * In order to support COW of arbitrary special mappings, we have VM_MIXEDMAP. * * VM_MIXEDMAP mappings can likewise contain memory with or without "struct * page" backing, however the difference is that _all_ pages with a struct @@ -407,16 +411,29 @@ static inline int is_cow_mapping(unsigned int flags) * advantage is that we don't have to follow the strict linearity rule of * PFNMAP mappings in order to support COWable mappings. * - * A call to vm_normal_page() with a VM_MIXEDMAP mapping will return the - * associated "struct page" or NULL for memory not backed by a "struct page". - * - * - * All other mappings should have a valid struct page, which will be - * returned by a call to vm_normal_page(). */ -struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_t pte) +#ifdef __HAVE_ARCH_PTE_SPECIAL +# define HAVE_PTE_SPECIAL 1 +#else +# define HAVE_PTE_SPECIAL 0 +#endif +struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, + pte_t pte) { - unsigned long pfn = pte_pfn(pte); + unsigned long pfn; + + if (HAVE_PTE_SPECIAL) { + if (likely(!pte_special(pte))) { + VM_BUG_ON(!pfn_valid(pte_pfn(pte))); + return pte_page(pte); + } + VM_BUG_ON(!(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))); + return NULL; + } + + /* !HAVE_PTE_SPECIAL case follows: */ + + pfn = pte_pfn(pte); if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) { if (vma->vm_flags & VM_MIXEDMAP) { @@ -424,7 +441,8 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_ return NULL; goto out; } else { - unsigned long off = (addr-vma->vm_start) >> PAGE_SHIFT; + unsigned long off; + off = (addr - vma->vm_start) >> PAGE_SHIFT; if (pfn == vma->vm_pgoff + off) return NULL; if (!is_cow_mapping(vma->vm_flags)) @@ -432,25 +450,12 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_ } } -#ifdef CONFIG_DEBUG_VM - /* - * Add some anal sanity checks for now. Eventually, - * we should just do "return pfn_to_page(pfn)", but - * in the meantime we check that we get a valid pfn, - * and that the resulting page looks ok. - */ - if (unlikely(!pfn_valid(pfn))) { - print_bad_pte(vma, pte, addr); - return NULL; - } -#endif + VM_BUG_ON(!pfn_valid(pfn)); /* - * NOTE! We still have PageReserved() pages in the page - * tables. + * NOTE! We still have PageReserved() pages in the page tables. * - * The PAGE_ZERO() pages and various VDSO mappings can - * cause them to exist. + * eg. VDSO mappings can cause them to exist. */ out: return pfn_to_page(pfn); @@ -1263,6 +1268,12 @@ int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr, pte_t *pte, entry; spinlock_t *ptl; + /* + * Technically, architectures with pte_special can avoid all these + * restrictions (same for remap_pfn_range). However we would like + * consistency in testing and feature parity among all, so we should + * try to keep these invariants in place for everybody. + */ BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))); BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) == (VM_PFNMAP|VM_MIXEDMAP)); @@ -1278,7 +1289,7 @@ int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr, goto out_unlock; /* Ok, finally just insert the thing.. */ - entry = pfn_pte(pfn, vma->vm_page_prot); + entry = pte_mkspecial(pfn_pte(pfn, vma->vm_page_prot)); set_pte_at(mm, addr, pte, entry); update_mmu_cache(vma, addr, entry); @@ -1309,7 +1320,7 @@ static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd, arch_enter_lazy_mmu_mode(); do { BUG_ON(!pte_none(*pte)); - set_pte_at(mm, addr, pte, pfn_pte(pfn, prot)); + set_pte_at(mm, addr, pte, pte_mkspecial(pfn_pte(pfn, prot))); pfn++; } while (pte++, addr += PAGE_SIZE, addr != end); arch_leave_lazy_mmu_mode(); |