linux-kernel - Re: [Qemu-devel PATCH] target/i386: define a new MSR based feature word

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Date:   Fri, 29 May 2020 12:23:59 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Like Xu <like.xu@...ux.intel.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Richard Henderson <rth@...ddle.net>,
        Eduardo Habkost <ehabkost@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>, qemu-devel@...gnu.org
Subject: Re: [Qemu-devel PATCH] target/i386: define a new MSR based feature
 word - FEAT_PERF_CAPABILITIES

On 29/05/20 09:43, Like Xu wrote:
> +        if (!cpu->enable_pmu) {
> +            *ecx &= ~CPUID_EXT_PDCM;
> +        }
>          break;
>      case 2:
>          /* cache info: needed for Pentium Pro compatibility */
> @@ -6505,6 +6528,12 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
>          }
>      }
>  
> +    if (kvm_enabled() && cpu->enable_pmu &&
> +        (kvm_arch_get_supported_cpuid(kvm_state, 1, 0, R_ECX) &
> +         CPUID_EXT_PDCM)) {
> +        env->features[FEAT_1_ECX] |= CPUID_EXT_PDCM;
> +    }
> +

I'm dropping this hunk two hunks because it's going to break live
migration with e.g. "-cpu IvyBridge,pmu=on".  We will have to add PDCM
by default only to future CPU models, but "-cpu host,pmu=on" will pick
it up automatically.

Paolo