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SubjectRe: [PATCH] KVM: X86: Do not yield to self
On Thu, Apr 08, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.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@tencent.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 you're going to bother with a comment, maybe elaborate a bit, e.g.

/* Ignore requests to yield to self. */

> + if (vcpu->vcpu_id == target->vcpu_id)
> + goto no_yield;
> +
> if (!READ_ONCE(target->ready))
> goto no_yield;
>
> --
> 2.7.4
>

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