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Subject: Re: [PATCH] KVM: x86: accept userspace interrupt only if no event is
 injected
To:     Paolo Bonzini <pbonzini@redhat.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     stable@vger.kernel.org
References: <20210714213846.854837-1-pbonzini@redhat.com>
From:   stsp <stsp2@yandex.ru>
Message-ID: <6f2305c0-77a8-42af-f5e9-2664119b6b2e@yandex.ru>
Date:   Fri, 16 Jul 2021 10:27:03 +0300
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15.07.2021 00:38, Paolo Bonzini пишет:
> Once an exception has been injected, any side effects related to
> the exception (such as setting CR2 or DR6) have been taked

"taken"? Probably a typo.


>   place.
> Therefore, once KVM sets the VM-entry interruption information
> field or the AMD EVENTINJ field, the next VM-entry must deliver that
> exception.
>
> Pending interrupts are processed after injected exceptions, so
> in theory it would not be a problem to use KVM_INTERRUPT when
> an injected exception is present.  However, DOSBox

dosemu2 to be precise.


>   is using
> run->ready_for_interrupt_injection to detect interrupt windows
> and then using KVM_SET_SREGS/KVM_SET_REGS to inject the
> interrupt manually.  For this to work, the interrupt window
> must be delayed after the completion of the previous event
> injection.
>
> Cc: stable@vger.kernel.org
> Reported-by: Stas Sergeev <stsp2@yandex.ru>
> Tested-by: Stas Sergeev <stsp2@yandex.ru>
> Fixes: 71cc849b7093 ("KVM: x86: Fix split-irqchip vs interrupt injection window request")
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   arch/x86/kvm/x86.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fe3aaf195292..7fbab29b3569 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4342,6 +4342,9 @@ static int kvm_vcpu_ioctl_set_lapic(struct kvm_vcpu *vcpu,
>   
>   static int kvm_cpu_accept_dm_intr(struct kvm_vcpu *vcpu)
>   {
> +	if (kvm_event_needs_reinjection(vcpu))
> +		return false;
> +

kvm_event_needs_reinjection() seems
to miss exception.pending check.
Don't we need it too?

Also perhaps a comment would be good
to have to avoid it from disappearing again,
as obviously kvm devs tend to overlook
the possibility of injecting interrupts by hands.