[v2,22/27] KVM: x86/mmu: skip over invalid root pages when zapping all sptes
diff mbox series

Message ID 20190205210137.1377-22-sean.j.christopherson@intel.com
State New
Headers show
Series
  • KVM: x86/mmu: Remove fast invalidate mechanism
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Commit Message

Sean Christopherson Feb. 5, 2019, 9:01 p.m. UTC
...to guarantee forward progress.  When zapped, root pages are marked
invalid and moved to the head of the active pages list until they are
explicitly freed.  Theoretically, having unzappable root pages at the
head of the list could prevent kvm_mmu_zap_all() from making forward
progress were a future patch to add a loop restart after processing a
page, e.g. to drop mmu_lock on contention.

Although kvm_mmu_prepare_zap_page() can theoretically take action on
invalid pages, e.g. to zap unsync children, functionally it's not
necessary (root pages will be re-zapped when freed) and practically
speaking the odds of e.g. @unsync or @unsync_children becoming %true
while zapping all pages is basically nil.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/mmu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Patch
diff mbox series

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index bdba6c85f81f..3ceabf3e7e0d 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5850,9 +5850,12 @@  void kvm_mmu_zap_all(struct kvm *kvm)
 
 	spin_lock(&kvm->mmu_lock);
 restart:
-	list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link)
+	list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) {
+		if (sp->role.invalid && sp->root_count)
+			continue;
 		if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list))
 			goto restart;
+	}
 
 	kvm_mmu_commit_zap_page(kvm, &invalid_list);
 	spin_unlock(&kvm->mmu_lock);