linux-kernel - [PATCH 11/11] KVM: x86/mmu: Skip invalid pages during zapping iff root

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Date:   Thu, 12 Sep 2019 19:46:12 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        James Harvey <jamespharvey20@...il.com>,
        Alex Willamson <alex.williamson@...hat.com>
Subject: [PATCH 11/11] KVM: x86/mmu: Skip invalid pages during zapping iff root_count is zero

Do not skip invalid shadow pages when zapping obsolete pages if the
pages' root_count has reached zero, in which case the page can be
immediately zapped and freed.

Update the comment accordingly.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/mmu.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index a7b14750cde9..5e41b1f77a6d 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5692,11 +5692,12 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm)
 			break;
 
 		/*
-		 * Since we are reversely walking the list and the invalid
-		 * list will be moved to the head, skip the invalid page
-		 * can help us to avoid the infinity list walking.
+		 * Skip invalid pages with a non-zero root count, zapping pages
+		 * with a non-zero root count will never succeed, i.e. the page
+		 * will get thrown back on active_mmu_pages and we'll get stuck
+		 * in an infinite loop.
 		 */
-		if (sp->role.invalid)
+		if (sp->role.invalid && sp->root_count)
 			continue;
 
 		/*
-- 
2.22.0