linux-kernel - Re: [PATCH 0/6] KVM: nVMX: Fix IPIv vs. nested posted interrupts

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Message-ID: <Zp7yDvcwfPtgED0j@google.com>
Date: Mon, 22 Jul 2024 16:58:06 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Chao Gao <chao.gao@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Zeng Guang <guang.zeng@...el.com>
Subject: Re: [PATCH 0/6] KVM: nVMX: Fix IPIv vs. nested posted interrupts

On Mon, Jul 22, 2024, Chao Gao wrote:
> On Fri, Jul 19, 2024 at 05:01:32PM -0700, Sean Christopherson wrote:
> >Fix a bug where KVM injects L2's nested posted interrupt into L1 as a
> >nested VM-Exit instead of triggering PI processing.  The actual bug is
> >technically a generic nested posted interrupts problem, but due to the
> >way that KVM handles interrupt delivery, I'm 99.9% certain the issue is
> >limited to IPI virtualization being enabled.
> 
> Theoretically VT-d posted interrupt can also trigger this issue.

Hmm, yeah, I think you're right.  L1 could program an assigned device to _post_
an interrupt to L2's vector, via L1's PID.PIR.  Which would let the interrupt
into vIRR without KVM checking vmcs12's NV.  It seems unlikely L1 would do that,
but it definitely seems possible.

Unless I'm missing something (else), I'll update the changelog and Fixes: to make
it clear that IPI virtualization just makes the bug easier to hit, but that the
issue exists with nested assigned devices, too.