linux-kernel - [PATCH] KVM: x86/MMU: Do not check unsync status for root SP.

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Date:   Sat, 16 Jan 2021 08:21:00 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     pbonzini@...hat.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        seanjc@...gle.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org
Subject: [PATCH] KVM: x86/MMU: Do not check unsync status for root SP.

In shadow page table, only leaf SPs may be marked as unsync.
And for non-leaf SPs, we use unsync_children to keep the number
of the unsynced children. In kvm_mmu_sync_root(), sp->unsync
shall always be zero for the root SP, hence no need to check it.

Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
---
 arch/x86/kvm/mmu/mmu.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6d16481a..1a6bb03 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3412,8 +3412,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
 		 * mmu_need_write_protect() describe what could go wrong if this
 		 * requirement isn't satisfied.
 		 */
-		if (!smp_load_acquire(&sp->unsync) &&
-		    !smp_load_acquire(&sp->unsync_children))
+		if (!smp_load_acquire(&sp->unsync_children))
 			return;
 
 		spin_lock(&vcpu->kvm->mmu_lock);
-- 
1.9.1