KVM: Simplify kvm->tlbs_dirty handling

When this was introduced, kvm_flush_remote_tlbs() could be called without holding mmu_lock. It is now acknowledged that the function must be called before releasing mmu_lock, and all callers have already been changed to do so. There is no need to use smp_mb() and cmpxchg() any more. Signed-off-by: Takuya Yoshikawa <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
kyagi · Feb 18, 2014 · 5befdc3 · 5befdc3
1 parent f18eb31
commit 5befdc3
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Showing 3 changed files with 8 additions and 8 deletions.
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
@@ -913,7 +913,8 @@ static gpa_t FNAME(gva_to_gpa_nested)(struct kvm_vcpu *vcpu, gva_t vaddr,
  *   and kvm_mmu_notifier_invalidate_range_start detect the mapping page isn't
  *   used by guest then tlbs are not flushed, so guest is allowed to access the
  *   freed pages.
- *   And we increase kvm->tlbs_dirty to delay tlbs flush in this case.
+ *   We set tlbs_dirty to let the notifier know this change and delay the flush
+ *   until such a case actually happens.
  */
 static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 {
@@ -942,7 +943,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 			return -EINVAL;
 
 		if (FNAME(prefetch_invalid_gpte)(vcpu, sp, &sp->spt[i], gpte)) {
-			vcpu->kvm->tlbs_dirty++;
+			vcpu->kvm->tlbs_dirty = true;
 			continue;
 		}
 
@@ -957,7 +958,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 
 		if (gfn != sp->gfns[i]) {
 			drop_spte(vcpu->kvm, &sp->spt[i]);
-			vcpu->kvm->tlbs_dirty++;
+			vcpu->kvm->tlbs_dirty = true;
 			continue;
 		}
 

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
@@ -401,7 +401,9 @@ struct kvm {
 	unsigned long mmu_notifier_seq;
 	long mmu_notifier_count;
 #endif
-	long tlbs_dirty;
+	/* Protected by mmu_lock */
+	bool tlbs_dirty;
+
 	struct list_head devices;
 };
 

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
@@ -186,12 +186,9 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
 
 void kvm_flush_remote_tlbs(struct kvm *kvm)
 {
-	long dirty_count = kvm->tlbs_dirty;
-
-	smp_mb();
 	if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
 		++kvm->stat.remote_tlb_flush;
-	cmpxchg(&kvm->tlbs_dirty, dirty_count, 0);
+	kvm->tlbs_dirty = false;
 }
 EXPORT_SYMBOL_GPL(kvm_flush_remote_tlbs);