Explicitly check if a NX huge page is disallowed when determining if a page
fault needs to be forced to use a smaller sized page. KVM incorrectly
assumes that the NX huge page mitigation is the only scenario where KVM
will create a shadow page instead of a huge page. Any scenario that causes
KVM to zap leaf SPTEs may result in having a SP that can be made huge
without violating the NX huge page mitigation. E.g. disabling of dirty
logging, zapping from mmu_notifier due to page migration, guest MTRR
changes that affect the viability of a huge page, etc...
Fixes: b8e8c8303ff2 ("kvm: mmu: ITLB_MULTIHIT mitigation")
Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 5cb845fae56e..033609e8b332 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2896,6 +2896,16 @@ void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_
cur_level == fault->goal_level &&
is_shadow_present_pte(spte) &&
!is_large_pte(spte)) {
+ struct kvm_mmu_page *sp;
+ u64 page_mask;
+
+ sp = to_shadow_page(spte & PT64_BASE_ADDR_MASK);
+
+ /* Prevent lpage_disallowed read from moving ahead. */
+ smp_rmb();
+
+ if (!sp->lpage_disallowed)
+ return;
/*
* A small SPTE exists for this pfn, but FNAME(fetch)
* and __direct_map would like to create a large PTE
@@ -2903,8 +2913,8 @@ void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_
* patching back for them into pfn the next 9 bits of
* the address.
*/
- u64 page_mask = KVM_PAGES_PER_HPAGE(cur_level) -
- KVM_PAGES_PER_HPAGE(cur_level - 1);
+ page_mask = KVM_PAGES_PER_HPAGE(cur_level) -
+ KVM_PAGES_PER_HPAGE(cur_level - 1);
fault->pfn |= fault->gfn & page_mask;
fault->goal_level--;
}
--
2.35.1.1094.g7c7d902a7c-goog
