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From:   Lai Jiangshan <jiangshanlai@gmail.com>
To:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        Lai Jiangshan <jiangshan.ljs@antgroup.com>
Subject: [PATCH 01/12] KVM: X86/MMU: Warn if sp->unsync_children > 0 in link_shadow_page()
Date:   Sun,  5 Jun 2022 14:43:31 +0800
Message-Id: <20220605064342.309219-2-jiangshanlai@gmail.com>
In-Reply-To: <20220605064342.309219-1-jiangshanlai@gmail.com>
References: <20220605064342.309219-1-jiangshanlai@gmail.com>
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From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

The check for sp->unsync_children in link_shadow_page() can be removed
since FNAME(fetch) ensures it is zero.  (@sp is direct when
link_shadow_page() is called from other places, which also means
sp->unsync_children is zero.)

link_shadow_page() is not a fast path, check it and warn instead.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
---
 arch/x86/kvm/mmu/mmu.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 086f32dffdbe..f61416818116 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2197,7 +2197,13 @@ static void link_shadow_page(struct kvm_vcpu *vcpu, u64 *sptep,
 
 	mmu_page_add_parent_pte(vcpu, sp, sptep);
 
-	if (sp->unsync_children || sp->unsync)
+	/*
+	 * Propagate the unsync bit when sp->unsync.
+	 *
+	 * The caller ensures the sp is synced when it has unsync children,
+	 * so sp->unsync_children must be zero.  See FNAME(fetch).
+	 */
+	if (sp->unsync || WARN_ON_ONCE(sp->unsync_children))
 		mark_unsync(sptep);
 }
 
-- 
2.19.1.6.gb485710b