[PATCH] KVM: X86: Do not yield to self

[Wanpeng Li]

From: Wanpeng Li <wanpengli@xxxxxxxxxxx>

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@xxxxxxxxxxx>
---
Rebased on https://lore.kernel.org/kvm/1617697935-4158-1-git-send-email-wanpengli@xxxxxxxxxxx/

 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