linux-kernel - Re: [PATCH 0/6] KVM/x86: Add workaround to support ExtINT with AVIC

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Date:   Fri, 5 Apr 2019 00:06:53 +0200
From:   "rkrcmar@...hat.com" <rkrcmar@...hat.com>
To:     "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>
Subject: Re: [PATCH 0/6] KVM/x86: Add workaround to support ExtINT with AVIC

2019-03-22 11:57+0000, Suthikulpanit, Suravee:
> This series is one of the prerequisites for supporting AMD AVIC with
> in-kernel irqchip (kernel_irqchip=on).
> 
> Since AVIC does not support ExtINT interrupt, which is required during
> the booting phase of Windows and FreeBSD VMs (e.g. PIT -> PIC -> ExtInt).
> This results in VM hang in the boot loader with kernel_irqchip=on mode.
> 
> This series provides workaround by temporary deactivate AVIC and fallback
> to use legacy interrupt injection (w/ vINTR and interrupt window).
> Then re-activate AVIC once the intrrupts are handled.

Hm, another idea.  It is possible to inject the ExtInt in APICv, but if
interrupt injection is currently disabled, we need to wait until the
interrupt window opens, which can't be done with int_* controls n.

Wouldn't intercepting IRET/STGI/IF writes be enough to eventually reach
the point where we can do event_inj?

Thanks.