linux-kernel - Re: [PATCH v19 040/130] KVM: TDX: Make pmu

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Date: Thu, 21 Mar 2024 10:46:31 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Chao Gao <chao.gao@...el.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 040/130] KVM: TDX: Make pmu_intel.c ignore guest TD
 case

On Wed, Mar 20, 2024 at 03:01:48PM +0800,
Chao Gao <chao.gao@...el.com> wrote:

> On Mon, Feb 26, 2024 at 12:25:42AM -0800, isaku.yamahata@...el.com wrote:
> >From: Isaku Yamahata <isaku.yamahata@...el.com>
> >
> >Because TDX KVM doesn't support PMU yet (it's future work of TDX KVM
> >support as another patch series) and pmu_intel.c touches vmx specific
> >structure in vcpu initialization, as workaround add dummy structure to
> >struct vcpu_tdx and pmu_intel.c can ignore TDX case.
> 
> Can we instead factor pmu_intel.c to avoid corrupting memory? how hard would it
> be?

Do you mean sprinkling "if (tdx) return"? It's easy. Just add it to all hooks
in kvm_pmu_ops.

I chose this approach because we'll soon support vPMU support. For simplicity,
will switch to sprinkle "if (tdx) return".

> >+bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu)
> >+{
> >+	struct x86_pmu_lbr *lbr = vcpu_to_lbr_records(vcpu);
> >+
> >+	if (is_td_vcpu(vcpu))
> >+		return false;
> >+
> >+	return lbr->nr && (vcpu_get_perf_capabilities(vcpu) & PMU_CAP_LBR_FMT);
> 
> The check about vcpu's perf capabilities is new. is it necessary?

No. Will delete it. It crept in during rebase.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>