Received-SPF: pass (google.com: domain of linux-kernel+bounces-141669-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Precedence: bulk
MIME-Version: 1.0
References: <20240126085444.324918-1-xiong.y.zhang@linux.intel.com>
 <20240126085444.324918-16-xiong.y.zhang@linux.intel.com> <ZhhUZJ7rE0SbE6Vv@google.com>
In-Reply-To: <ZhhUZJ7rE0SbE6Vv@google.com>
From: Jim Mattson <jmattson@google.com>
Date: Thu, 11 Apr 2024 15:30:32 -0700
Message-ID: <CALMp9eQ01NJZKKYt8XhTbnu8rNpuhpk388ocvyPqWJiO+sov5g@mail.gmail.com>
Subject: Re: [RFC PATCH 15/41] KVM: x86/pmu: Manage MSR interception for IA32_PERF_GLOBAL_CTRL
To: Sean Christopherson <seanjc@google.com>
Cc: Xiong Zhang <xiong.y.zhang@linux.intel.com>, pbonzini@redhat.com, 
	peterz@infradead.org, mizhang@google.com, kan.liang@intel.com, 
	zhenyuw@linux.intel.com, dapeng1.mi@linux.intel.com, kvm@vger.kernel.org, 
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, 
	zhiyuan.lv@intel.com, eranian@google.com, irogers@google.com, 
	samantha.alt@intel.com, like.xu.linux@gmail.com, chao.gao@intel.com, 
	Xiong Zhang <xiong.y.zhang@intel.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Thu, Apr 11, 2024 at 2:21=E2=80=AFPM Sean Christopherson <seanjc@google.=
com> wrote:
>
> On Fri, Jan 26, 2024, Xiong Zhang wrote:
> > +     if (is_passthrough_pmu_enabled(&vmx->vcpu)) {
> > +             /*
> > +              * Setup auto restore guest PERF_GLOBAL_CTRL MSR at vm en=
try.
> > +              */
> > +             if (vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL)
> > +                     vmcs_write64(GUEST_IA32_PERF_GLOBAL_CTRL, 0);
> > +             else {
> > +                     i =3D vmx_find_loadstore_msr_slot(&vmx->msr_autol=
oad.guest,
> > +                                                    MSR_CORE_PERF_GLOB=
AL_CTRL);
> > +                     if (i < 0) {
> > +                             i =3D vmx->msr_autoload.guest.nr++;
> > +                             vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT,
> > +                                          vmx->msr_autoload.guest.nr);
> > +                     }
> > +                     vmx->msr_autoload.guest.val[i].index =3D MSR_CORE=
_PERF_GLOBAL_CTRL;
> > +                     vmx->msr_autoload.guest.val[i].value =3D 0;
>
> Eww, no.   Just make cpu_has_load_perf_global_ctrl() and VM_EXIT_SAVE_IA3=
2_PERF_GLOBAL_CTRL
> hard requirements for enabling passthrough mode.  And then have clear_ato=
mic_switch_msr()
> yell if KVM tries to disable loading MSR_CORE_PERF_GLOBAL_CTRL.

Weren't you just complaining about the PMU version 4 constraint in
another patch? And here, you are saying, "Don't support anything older
than Sapphire Rapids."

Sapphire Rapids has PMU version 4, so if we require
VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL, PMU version 4 is irrelevant.