linux-kernel - Re: [RFC PATCH v4 6/7] KVM: x86: Add a new guest

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Date:   Wed, 20 Jul 2022 17:06:07 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Kechen Lu <kechenl@...dia.com>
Cc:     kvm@...r.kernel.org, pbonzini@...hat.com, chao.gao@...el.com,
        vkuznets@...hat.com, somduttar@...dia.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v4 6/7] KVM: x86: Add a new guest_debug flag forcing
 exit to userspace

On Tue, Jun 21, 2022, Kechen Lu wrote:
> For debug and test purposes, there are needs to explicitly make
> instruction triggered exits could be trapped to userspace. Simply
> add a new flag for guest_debug interface could achieve this.
> 
> This patch also fills the userspace accessible field
> vcpu->run->hw.hardware_exit_reason for userspace to determine the
> original triggered VM-exits.

This patch belongs in a different series, AFAICT there are no dependencies between
this and allowing per-vCPU disabling of exits.  Allowing userspace to exit on
"every" instruction exit is going to be much more controversial, largely because
it will be difficult for KVM to provide a consistent, robust ABI.  E.g. should
KVM exit to userspace if an intercepted instruction is encountered by the emualtor?

TL;DR: drop this patch from the next version.