Re: [PATCH v6 03/19] i386: always fill Hyper-V CPUID feature leaves from X86CPU data

[Eduardo Habkost]

On Thu, Apr 22, 2021 at 06:11:14PM +0200, Vitaly Kuznetsov wrote:
> We have all the required data in X86CPU already and as we are about to
> split hyperv_handle_properties() into hyperv_expand_features()/
> hyperv_fill_cpuids() we can remove the blind copy. The functional change
> is that QEMU won't pass CPUID leaves it doesn't currently know about
> to the guest but arguably this is a good change.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>

This makes hv-passthrough less useful for debugging and
development, but safer for using in production.  I assume we want
to eventually make hv-passthrough supported in production when
live migration support isn't required.

I'll trust your judgement here and assume this is really a good
change, but maybe this should be documented more explicitly in
the hv-passthrough section at docs/hyperv.txt?

Anyway:

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>

> ---
>  target/i386/kvm/kvm.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index afd173514da1..7c751185491f 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -1207,9 +1207,6 @@ static int hyperv_handle_properties(CPUState *cs,
>      }
>  
>      if (cpu->hyperv_passthrough) {
> -        memcpy(cpuid_ent, &cpuid->entries[0],
> -               cpuid->nent * sizeof(cpuid->entries[0]));
> -
>          c = cpuid_find_entry(cpuid, HV_CPUID_VENDOR_AND_MAX_FUNCTIONS, 0);
>          if (c) {
>              cpu->hyperv_vendor_id[0] = c->ebx;
> @@ -1309,12 +1306,6 @@ static int hyperv_handle_properties(CPUState *cs,
>          goto free;
>      }
>  
> -    if (cpu->hyperv_passthrough) {
> -        /* We already copied all feature words from KVM as is */
> -        r = cpuid->nent;
> -        goto free;
> -    }
> -
>      c = &cpuid_ent[cpuid_i++];
>      c->function = HV_CPUID_VENDOR_AND_MAX_FUNCTIONS;
>      c->eax = hyperv_feat_enabled(cpu, HYPERV_FEAT_EVMCS) ?
> -- 
> 2.30.2
> 

-- 
Eduardo