From 08fe1e7bd216339501c4eb0d0df0f413d715327a Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Wed, 24 Jun 2015 21:18:06 +1000 Subject: KVM: PPC: Book3S HV: Fix bug in dirty page tracking This fixes a bug in the tracking of pages that get modified by the guest. If the guest creates a large-page HPTE, writes to memory somewhere within the large page, and then removes the HPTE, we only record the modified state for the first normal page within the large page, when in fact the guest might have modified some other normal page within the large page. To fix this we use some unused bits in the rmap entry to record the order (log base 2) of the size of the page that was modified, when removing an HPTE. Then in kvm_test_clear_dirty_npages() we use that order to return the correct number of modified pages. The same thing could in principle happen when removing a HPTE at the host's request, i.e. when paging out a page, except that we never page out large pages, and the guest can only create large-page HPTEs if the guest RAM is backed by large pages. However, we also fix this case for the sake of future-proofing. The reference bit is also subject to the same loss of information. We don't make the same fix here for the reference bit because there isn't an interface for userspace to find out which pages the guest has referenced, whereas there is one for userspace to find out which pages the guest has modified. Because of this loss of information, the kvm_age_hva_hv() and kvm_test_age_hva_hv() functions might incorrectly say that a page has not been referenced when it has, but that doesn't matter greatly because we never page or swap out large pages. Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf --- arch/powerpc/include/asm/kvm_book3s.h | 1 + 1 file changed, 1 insertion(+) (limited to 'arch/powerpc/include/asm/kvm_book3s.h') diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h index b91e74a817d8..e6b2534a2a63 100644 --- a/arch/powerpc/include/asm/kvm_book3s.h +++ b/arch/powerpc/include/asm/kvm_book3s.h @@ -158,6 +158,7 @@ extern pfn_t kvmppc_gpa_to_pfn(struct kvm_vcpu *vcpu, gpa_t gpa, bool writing, bool *writable); extern void kvmppc_add_revmap_chain(struct kvm *kvm, struct revmap_entry *rev, unsigned long *rmap, long pte_index, int realmode); +extern void kvmppc_update_rmap_change(unsigned long *rmap, unsigned long psize); extern void kvmppc_invalidate_hpte(struct kvm *kvm, __be64 *hptep, unsigned long pte_index); void kvmppc_clear_ref_hpte(struct kvm *kvm, __be64 *hptep, -- cgit v1.2.3