From fce0657ff9f14f6b1f147b5fcd6db2f54c06424e Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Tue, 1 May 2007 16:44:05 +0300 Subject: [PATCH] KVM: MMU: Respect nonpae pagetable quadrant when zapping ptes When a guest writes to a page that has an mmu shadow, we have to clear the shadow pte corresponding to the memory location touched by the guest. Now, in nonpae mode, a single guest page may have two or four shadow pages (because a nonpae page maps 4MB or 4GB, whereas the pae shadow maps 2MB or 1GB), so we when we look up the page we find up to three additional aliases for the page. Since we _clear_ the shadow pte, it doesn't matter except for a slight performance penalty, but if we want to _update_ the shadow pte instead of clearing it, it is vital that we don't modify the aliases. Fortunately, exactly which page is needed (the "quadrant") is easily computed, and is accessible in the shadow page header. All we need is to ignore shadow pages from the wrong quadrants. Signed-off-by: Avi Kivity --- drivers/kvm/mmu.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c index b3a83ef2cf07..23dc4612026b 100644 --- a/drivers/kvm/mmu.c +++ b/drivers/kvm/mmu.c @@ -1150,6 +1150,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned pte_size; unsigned page_offset; unsigned misaligned; + unsigned quadrant; int level; int flooded = 0; int npte; @@ -1202,7 +1203,10 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa, page_offset <<= 1; npte = 2; } + quadrant = page_offset >> PAGE_SHIFT; page_offset &= ~PAGE_MASK; + if (quadrant != page->role.quadrant) + continue; } spte = __va(page->page_hpa); spte += page_offset / sizeof(*spte); -- 2.20.1