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Subject[PATCH v2 3/6] KVM: MMU: fix page dirty tracking lost while sync page
In sync-page path, if spte.writable is changed, it will lose page dirty
tracking, for example:

assume spte.writable = 0 in a unsync-page, when it's synced, it map spte
to writable(that is spte.writable = 1), later guest write spte.gfn, it means
spte.gfn is dirty, then guest changed this mapping to read-only, after it's
synced, spte.writable = 0

So, when host release the spte, it detect spte.writable = 0 and not mark page
dirty

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
arch/x86/kvm/mmu.c | 10 +++-------
1 files changed, 3 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 5937054..b3896bf 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1981,6 +1981,8 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
mark_page_dirty(vcpu->kvm, gfn);

set_pte:
+ if (is_writable_pte(*sptep) && !is_writable_pte(spte))
+ kvm_set_pfn_dirty(pfn);
update_spte(sptep, spte);
done:
return ret;
@@ -1994,7 +1996,6 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
bool reset_host_protection)
{
int was_rmapped = 0;
- int was_writable = is_writable_pte(*sptep);
int rmap_count;

pgprintk("%s: spte %llx access %x write_fault %d"
@@ -2044,15 +2045,10 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
page_header_update_slot(vcpu->kvm, sptep, gfn);
if (!was_rmapped) {
rmap_count = rmap_add(vcpu, sptep, gfn);
- kvm_release_pfn_clean(pfn);
if (rmap_count > RMAP_RECYCLE_THRESHOLD)
rmap_recycle(vcpu, sptep, gfn);
- } else {
- if (was_writable)
- kvm_release_pfn_dirty(pfn);
- else
- kvm_release_pfn_clean(pfn);
}
+ kvm_release_pfn_clean(pfn);
if (speculative) {
vcpu->arch.last_pte_updated = sptep;
vcpu->arch.last_pte_gfn = gfn;
--
1.6.1.2




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