linux-kernel - Re: [PATCH v2 0/5] KVM: Fix oneshot interrupts forwarding

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Message-ID: <d8704ffa-8d9e-2261-1bcf-1b402f955fad@redhat.com>
Date:   Thu, 11 Aug 2022 08:48:21 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Dmytro Maluka <dmy@...ihalf.com>, Marc Zyngier <maz@...nel.org>,
        eric.auger@...hat.com
Cc:     "Dong, Eddie" <eddie.dong@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Liu, Rong L" <rong.l.liu@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Grzegorz Jaszczyk <jaz@...ihalf.com>,
        "upstream@...ihalf.com" <upstream@...ihalf.com>,
        Dmitry Torokhov <dtor@...gle.com>
Subject: Re: [PATCH v2 0/5] KVM: Fix oneshot interrupts forwarding

On 8/10/22 19:02, Dmytro Maluka wrote:
>      1. If vEOI happens for a masked vIRQ, notify resamplefd as usual,
>         but also remember this vIRQ as, let's call it, "pending oneshot".
> 
>      2. A new physical IRQ is immediately generated, so the vIRQ is
>         properly set as pending.
> 
>      3. After the vIRQ is unmasked by the guest, check and find out that
>         it is not just pending but also "pending oneshot", so don't
>         deliver it to a vCPU. Instead, immediately notify resamplefd once
>         again.
> 
> In other words, don't avoid extra physical interrupts in the host
> (rather, use those extra interrupts for properly updating the pending
> state of the vIRQ) but avoid propagating those extra interrupts to the
> guest.
> 
> Does this sound reasonable to you?

Yeah, this makes sense and it lets the resamplefd set the "pending" 
status in the vGIC.  It still has the issue that the interrupt can 
remain pending in the guest for longer than it's pending on the host, 
but that can't be fixed?

Paolo