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Message-ID: <de73f4d1-7ec0-249b-5227-32ba78980c93@maciej.szmigiero.name>
Date:   Mon, 4 Apr 2022 22:27:26 +0200
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Subject: Re: [PATCH 6/8] KVM: SVM: Re-inject INTn instead of retrying the insn
 on "failure"
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To:     Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20220402010903.727604-1-seanjc@google.com>
 <20220402010903.727604-7-seanjc@google.com>
From:   "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
In-Reply-To: <20220402010903.727604-7-seanjc@google.com>
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On 2.04.2022 03:09, Sean Christopherson wrote:
> Re-inject INTn software interrupts instead of retrying the instruction if
> the CPU encountered an intercepted exception while vectoring the INTn,
> e.g. if KVM intercepted a #PF when utilizing shadow paging.  Retrying the
> instruction is architecturally wrong e.g. will result in a spurious #DB
> if there's a code breakpoint on the INT3/O, and lack of re-injection also
> breaks nested virtualization, e.g. if L1 injects a software interrupt and
> vectoring the injected interrupt encounters an exception that is
> intercepted by L0 but not L1.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/x86/kvm/svm/svm.c | 16 +++++++++++++++-
>   1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index ecc828d6921e..00b1399681d1 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3425,14 +3425,24 @@ static void svm_inject_nmi(struct kvm_vcpu *vcpu)
>   static void svm_inject_irq(struct kvm_vcpu *vcpu)
>   {
>   	struct vcpu_svm *svm = to_svm(vcpu);
> +	u32 type;
>   
>   	WARN_ON(!gif_set(svm));
>   
> +	if (vcpu->arch.interrupt.soft) {

It should be possible to inject soft interrupts even with GIF masked,
looked at the relevant code at patch 3 from my series [1].

Thanks,
Maciej

[1]: https://lore.kernel.org/kvm/a28577564a7583c32f0029f2307f63ca8869cf22.1646944472.git.maciej.szmigiero@oracle.com/