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authorTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>2012-05-09 16:10:39 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-05-12 09:32:19 -0700
commit87a6c3e2b97b6556a7184a198d7b862b101c24cd (patch)
parentf6a0ce750df3fd54adbdbfbaf9f0736763f4f7ac (diff)
KVM: Fix write protection race during dirty logging
(cherry picked from commit 6dbf79e7164e9a86c1e466062c48498142ae6128) This patch fixes a race introduced by: commit 95d4c16ce78cb6b7549a09159c409d52ddd18dae KVM: Optimize dirty logging by rmap_write_protect() During protecting pages for dirty logging, other threads may also try to protect a page in mmu_sync_children() or kvm_mmu_get_page(). In such a case, because get_dirty_log releases mmu_lock before flushing TLB's, the following race condition can happen: A (get_dirty_log) B (another thread) lock(mmu_lock) clear pte.w unlock(mmu_lock) lock(mmu_lock) pte.w is already cleared unlock(mmu_lock) skip TLB flush return ... TLB flush Though thread B assumes the page has already been protected when it returns, the remaining TLB entry will break that assumption. This patch fixes this problem by making get_dirty_log hold the mmu_lock until it flushes the TLB's. Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 5 insertions, 6 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9cbfc0698118..410b6b0565ab 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2997,6 +2997,8 @@ static void write_protect_slot(struct kvm *kvm,
unsigned long *dirty_bitmap,
unsigned long nr_dirty_pages)
+ spin_lock(&kvm->mmu_lock);
/* Not many dirty pages compared to # of shadow pages. */
if (nr_dirty_pages < kvm->arch.n_used_mmu_pages) {
unsigned long gfn_offset;
@@ -3004,16 +3006,13 @@ static void write_protect_slot(struct kvm *kvm,
for_each_set_bit(gfn_offset, dirty_bitmap, memslot->npages) {
unsigned long gfn = memslot->base_gfn + gfn_offset;
- spin_lock(&kvm->mmu_lock);
kvm_mmu_rmap_write_protect(kvm, gfn, memslot);
- spin_unlock(&kvm->mmu_lock);
- } else {
- spin_lock(&kvm->mmu_lock);
+ } else
kvm_mmu_slot_remove_write_access(kvm, memslot->id);
- spin_unlock(&kvm->mmu_lock);
- }
+ spin_unlock(&kvm->mmu_lock);