Date: Wed, 21 Nov 2018 10:50:08 -0200
From: Eduardo Habkost <ehabkost@redhat.com>
Message-ID: <20181121125008.GV4755@habkost.net>
References: <7280.1542702495@dschgrazlin2.units.it>
	<jpgd0qz3vg4.fsf@linux.bootlegged.copy>
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Subject: Re: [Qemu-devel] 3.1.0-rc{0,1} doesn't start
To: Bandan Das <bsd@redhat.com>
Cc: balducci@units.it, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, Laine Stump <laine@redhat.com>, David Alan Gilbert <dgilbert@redhat.com>, Cole Robinson <crobinso@redhat.com>

On Tue, Nov 20, 2018 at 11:28:59PM -0500, Bandan Das wrote:
> balducci@units.it writes:
> 
> > hello
> >
> >> incomplete because it can return 0 for data. Can you try this:
> >>
> >> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> >> index f524e7d929..4878ffb90b 100644
> >> --- a/target/i386/kvm.c
> >> +++ b/target/i386/kvm.c
> >> @@ -2002,14 +2002,9 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
> >>  #endif
> >>  
> >>      /* If host supports feature MSR, write down. */
> >> -    if (kvm_feature_msrs) {
> >> -        int i;
> >> -        for (i = 0; i < kvm_feature_msrs->nmsrs; i++)
> >> -            if (kvm_feature_msrs->indices[i] == MSR_IA32_ARCH_CAPABILITIES) 
> >> {
> >> -                kvm_msr_entry_add(cpu, MSR_IA32_ARCH_CAPABILITIES,
> >> +    if (kvm_arch_get_supported_msr_feature(kvm_state, MSR_IA32_ARCH_CAPABILI
> >> TIES)) {
> >> +        kvm_msr_entry_add(cpu, MSR_IA32_ARCH_CAPABILITIES,
> >>                                env->features[FEAT_ARCH_CAPABILITIES]);
> >> -                break;
> >> -            }
> >>      }
> >>  
> >>      /*
> >
> Sorry Gabriele, Eduardo and Paolo pointed out that the patch was incomplete.
> I am not sure however how you are getting non zero data with the rdmsr on an AMD.
> Can you please try this instead ?
> 
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index f524e7d929..cfec559aa3 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -95,6 +95,7 @@ static bool has_msr_xss;
>  static bool has_msr_spec_ctrl;
>  static bool has_msr_virt_ssbd;
>  static bool has_msr_smi_count;
> +static bool has_msr_arch_capabs;
>  
>  static uint32_t has_architectural_pmu_version;
>  static uint32_t num_architectural_pmu_gp_counters;
> @@ -1481,6 +1482,9 @@ static int kvm_get_supported_msrs(KVMState *s)
>                  case MSR_VIRT_SSBD:
>                      has_msr_virt_ssbd = true;
>                      break;
> +                case MSR_IA32_ARCH_CAPABILITIES:
> +                    has_msr_arch_capabs = true;
> +                    break;
>                  }
>              }
>          }
> @@ -2002,14 +2006,10 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
>  #endif
>  
>      /* If host supports feature MSR, write down. */
> -    if (kvm_feature_msrs) {
> -        int i;
> -        for (i = 0; i < kvm_feature_msrs->nmsrs; i++)
> -            if (kvm_feature_msrs->indices[i] == MSR_IA32_ARCH_CAPABILITIES) {
> +    if (kvm_arch_get_supported_msr_feature(kvm_state, MSR_IA32_ARCH_CAPABILITIES)
> +        && has_msr_arch_capabs) {

Unless we have a KVM bug too, has_msr_arch_capabs should be
enough.

If has_msr_arch_capabs is not enough, we'll need to add a comment
explaining why, or we risk reintroducing the same bug later.


>                  kvm_msr_entry_add(cpu, MSR_IA32_ARCH_CAPABILITIES,
>                                env->features[FEAT_ARCH_CAPABILITIES]);
> -                break;
> -            }
>      }
>  
>      /*
> 
> 

-- 
Eduardo