linux-kernel - [PATCH] KVM: X86: Do not yield to self

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Date:   Thu,  8 Apr 2021 19:23:09 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH] KVM: X86: Do not yield to self

From: Wanpeng Li <wanpengli@...cent.com>

If the target is self we do not need to yield, we can avoid malicious 
guest to play this.

Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
Rebased on https://lore.kernel.org/kvm/1617697935-4158-1-git-send-email-wanpengli@tencent.com/

 arch/x86/kvm/x86.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 43c9f9b..260650f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8230,6 +8230,10 @@ static void kvm_sched_yield(struct kvm_vcpu *vcpu, unsigned long dest_id)
 	if (!target)
 		goto no_yield;
 
+	/* yield to self */
+	if (vcpu->vcpu_id == target->vcpu_id)
+		goto no_yield;
+
 	if (!READ_ONCE(target->ready))
 		goto no_yield;
 
-- 
2.7.4