Received-SPF: pass (google.com: domain of linux-kernel+bounces-141646-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Thu, 11 Apr 2024 14:54:09 -0700
In-Reply-To: <20240126085444.324918-29-xiong.y.zhang@linux.intel.com>
Precedence: bulk
Mime-Version: 1.0
References: <20240126085444.324918-1-xiong.y.zhang@linux.intel.com> <20240126085444.324918-29-xiong.y.zhang@linux.intel.com>
Message-ID: <ZhhcAT7XiLHK3ZNQ@google.com>
Subject: Re: [RFC PATCH 28/41] KVM: x86/pmu: Switch IA32_PERF_GLOBAL_CTRL at
 VM boundary
From: Sean Christopherson <seanjc@google.com>
To: Xiong Zhang <xiong.y.zhang@linux.intel.com>
Cc: pbonzini@redhat.com, peterz@infradead.org, mizhang@google.com, 
	kan.liang@intel.com, zhenyuw@linux.intel.com, dapeng1.mi@linux.intel.com, 
	jmattson@google.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="us-ascii"

On Fri, Jan 26, 2024, Xiong Zhang wrote:
> +static void save_perf_global_ctrl_in_passthrough_pmu(struct vcpu_vmx *vmx)
> +{
> +	struct kvm_pmu *pmu = vcpu_to_pmu(&vmx->vcpu);
> +	int i;
> +
> +	if (vm_exit_controls_get(vmx) & VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL) {
> +		pmu->global_ctrl = vmcs_read64(GUEST_IA32_PERF_GLOBAL_CTRL);
> +	} else {
> +		i = vmx_find_loadstore_msr_slot(&vmx->msr_autostore.guest,
> +						MSR_CORE_PERF_GLOBAL_CTRL);
> +		if (i < 0)
> +			return;
> +		pmu->global_ctrl = vmx->msr_autostore.guest.val[i].value;

As before, NAK to using the MSR load/store lists unless there's a *really* good
reason I'm missing.

And we should consider adding VCPU_EXREG_GLOBAL_CTRL so that we can defer the
VMREAD until KVM actually tries to access the guest value.