linux-kernel - Re: [PATCH v3 1/4] KVM: x86: refactor req_immediate

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Date:   Fri, 24 Nov 2023 17:07:36 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v3 1/4] KVM: x86: refactor req_immediate_exit logic

On 9/28/23 12:36, Maxim Levitsky wrote:
> @@ -4176,6 +4176,9 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
>   	clgi();
>   	kvm_load_guest_xsave_state(vcpu);
>   
> +	if (vcpu->arch.req_immediate_exit)
> +		smp_send_reschedule(vcpu->cpu);
> +

This code is in a non-standard situation where IF=1 but interrupts are
effectively disabled.  Better something like:

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index beea99c8e8e0..3b945de2d880 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4148,8 +4148,11 @@ static __no_kcsan fastpath_t svm_vcpu_run(
  		 * is enough to force an immediate vmexit.
  		 */
  		disable_nmi_singlestep(svm);
+		vcpu->arch.req_immediate_exit = true;
+	}
+
+	if (vcpu->arch.req_immediate_exit)
  		smp_send_reschedule(vcpu->cpu);
-	}

  	pre_svm_run(vcpu);


Paolo