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From:   Kechen Lu <kechenl@nvidia.com>
To:     Sean Christopherson <seanjc@google.com>
CC:     "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "chao.gao@intel.com" <chao.gao@intel.com>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>,
        Somdutta Roy <somduttar@nvidia.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [RFC PATCH v4 6/7] KVM: x86: Add a new guest_debug flag forcing
 exit to userspace
Thread-Topic: [RFC PATCH v4 6/7] KVM: x86: Add a new guest_debug flag forcing
 exit to userspace
Thread-Index: AQHYhdK5aqHflcCxi0GPdL5WahEIoa2HqluAgAAhbxA=
Date:   Wed, 20 Jul 2022 19:11:18 +0000
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References: <20220622004924.155191-1-kechenl@nvidia.com>
 <20220622004924.155191-7-kechenl@nvidia.com> <Ytg1/zdSPYQ2lYS/@google.com>
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> -----Original Message-----
> From: Sean Christopherson <seanjc@google.com>
> Sent: Wednesday, July 20, 2022 10:06 AM
> To: Kechen Lu <kechenl@nvidia.com>
> Cc: kvm@vger.kernel.org; pbonzini@redhat.com; chao.gao@intel.com;
> vkuznets@redhat.com; Somdutta Roy <somduttar@nvidia.com>; linux-
> kernel@vger.kernel.org
> Subject: Re: [RFC PATCH v4 6/7] KVM: x86: Add a new guest_debug flag
> forcing exit to userspace
>=20
> External email: Use caution opening links or attachments
>=20
>=20
> 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.
>=20
> This patch belongs in a different series, AFAICT there are no dependencie=
s
> between this and allowing per-vCPU disabling of exits.  Allowing userspac=
e 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, rob=
ust ABI.
> E.g. should KVM exit to userspace if an intercepted instruction is
> encountered by the emualtor?
>=20
> TL;DR: drop this patch from the next version.

Ack. This patch I introduced as prerequisite for the patch 7 of implementin=
g the selftests for KVM_CAP_X86_DISABLE_EXITS. But yeah, it's not a good pr=
actice, I will try to think about a better way to implement the disabled ex=
its testing.

BR,
Kechen