From 8a674adc11cd4cc59e51eaea6f0cc4b3d5710411 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <sean.j.christopherson@intel.com>
Date: Tue, 5 Feb 2019 13:01:32 -0800
Subject: [PATCH] KVM: x86/mmu: skip over invalid root pages when zapping all
sptes
...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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/mmu.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 5cdeb88850f8f..c79ad7f31fdb2 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5853,9 +5853,12 @@ 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);
--
2.30.2