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authorMarc Zyngier <marc.zyngier@arm.com>2015-03-10 19:06:59 +0000
committerChristoffer Dall <christoffer.dall@linaro.org>2015-03-11 14:23:20 +0100
commita987370f8e7a1677ae385042644326d9cd145a20 (patch)
treebe11b7e7eac43314ff7ba8715c72bbdecdc905fb /arch/arm64
parentbfb8fb4775d3397908ae3a7ff65807097d81d713 (diff)
downloadlinux-a987370f8e7a1677ae385042644326d9cd145a20.tar.bz2
arm64: KVM: Fix stage-2 PGD allocation to have per-page refcounting
We're using __get_free_pages with to allocate the guest's stage-2 PGD. The standard behaviour of this function is to return a set of pages where only the head page has a valid refcount. This behaviour gets us into trouble when we're trying to increment the refcount on a non-head page: page:ffff7c00cfb693c0 count:0 mapcount:0 mapping: (null) index:0x0 flags: 0x4000000000000000() page dumped because: VM_BUG_ON_PAGE((*({ __attribute__((unused)) typeof((&page->_count)->counter) __var = ( typeof((&page->_count)->counter)) 0; (volatile typeof((&page->_count)->counter) *)&((&page->_count)->counter); })) <= 0) BUG: failure at include/linux/mm.h:548/get_page()! Kernel panic - not syncing: BUG! CPU: 1 PID: 1695 Comm: kvm-vcpu-0 Not tainted 4.0.0-rc1+ #3825 Hardware name: APM X-Gene Mustang board (DT) Call trace: [<ffff80000008a09c>] dump_backtrace+0x0/0x13c [<ffff80000008a1e8>] show_stack+0x10/0x1c [<ffff800000691da8>] dump_stack+0x74/0x94 [<ffff800000690d78>] panic+0x100/0x240 [<ffff8000000a0bc4>] stage2_get_pmd+0x17c/0x2bc [<ffff8000000a1dc4>] kvm_handle_guest_abort+0x4b4/0x6b0 [<ffff8000000a420c>] handle_exit+0x58/0x180 [<ffff80000009e7a4>] kvm_arch_vcpu_ioctl_run+0x114/0x45c [<ffff800000099df4>] kvm_vcpu_ioctl+0x2e0/0x754 [<ffff8000001c0a18>] do_vfs_ioctl+0x424/0x5c8 [<ffff8000001c0bfc>] SyS_ioctl+0x40/0x78 CPU0: stopping A possible approach for this is to split the compound page using split_page() at allocation time, and change the teardown path to free one page at a time. It turns out that alloc_pages_exact() and free_pages_exact() does exactly that. While we're at it, the PGD allocation code is reworked to reduce duplication. This has been tested on an X-Gene platform with a 4kB/48bit-VA host kernel, and kvmtool hacked to place memory in the second page of the hardware PGD (PUD for the host kernel). Also regression-tested on a Cubietruck (Cortex-A7). [ Reworked to use alloc_pages_exact() and free_pages_exact() and to return pointers directly instead of by reference as arguments - Christoffer ] Reported-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Diffstat (limited to 'arch/arm64')
-rw-r--r--arch/arm64/include/asm/kvm_mmu.h46
1 files changed, 4 insertions, 42 deletions
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 6458b5373142..a099cd9cdef8 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -171,43 +171,6 @@ static inline bool kvm_s2pmd_readonly(pmd_t *pmd)
#define KVM_PREALLOC_LEVEL (0)
#endif
-/**
- * kvm_prealloc_hwpgd - allocate inital table for VTTBR
- * @kvm: The KVM struct pointer for the VM.
- * @pgd: The kernel pseudo pgd
- *
- * When the kernel uses more levels of page tables than the guest, we allocate
- * a fake PGD and pre-populate it to point to the next-level page table, which
- * will be the real initial page table pointed to by the VTTBR.
- *
- * When KVM_PREALLOC_LEVEL==2, we allocate a single page for the PMD and
- * the kernel will use folded pud. When KVM_PREALLOC_LEVEL==1, we
- * allocate 2 consecutive PUD pages.
- */
-static inline int kvm_prealloc_hwpgd(struct kvm *kvm, pgd_t *pgd)
-{
- unsigned int i;
- unsigned long hwpgd;
-
- if (KVM_PREALLOC_LEVEL == 0)
- return 0;
-
- hwpgd = __get_free_pages(GFP_KERNEL | __GFP_ZERO, PTRS_PER_S2_PGD_SHIFT);
- if (!hwpgd)
- return -ENOMEM;
-
- for (i = 0; i < PTRS_PER_S2_PGD; i++) {
- if (KVM_PREALLOC_LEVEL == 1)
- pgd_populate(NULL, pgd + i,
- (pud_t *)hwpgd + i * PTRS_PER_PUD);
- else if (KVM_PREALLOC_LEVEL == 2)
- pud_populate(NULL, pud_offset(pgd, 0) + i,
- (pmd_t *)hwpgd + i * PTRS_PER_PMD);
- }
-
- return 0;
-}
-
static inline void *kvm_get_hwpgd(struct kvm *kvm)
{
pgd_t *pgd = kvm->arch.pgd;
@@ -224,12 +187,11 @@ static inline void *kvm_get_hwpgd(struct kvm *kvm)
return pmd_offset(pud, 0);
}
-static inline void kvm_free_hwpgd(struct kvm *kvm)
+static inline unsigned int kvm_get_hwpgd_size(void)
{
- if (KVM_PREALLOC_LEVEL > 0) {
- unsigned long hwpgd = (unsigned long)kvm_get_hwpgd(kvm);
- free_pages(hwpgd, PTRS_PER_S2_PGD_SHIFT);
- }
+ if (KVM_PREALLOC_LEVEL > 0)
+ return PTRS_PER_S2_PGD * PAGE_SIZE;
+ return PTRS_PER_S2_PGD * sizeof(pgd_t);
}
static inline bool kvm_page_empty(void *ptr)