Re: [Qemu-devel] [PATCH 4/8] target-i386: kvm_cpu_fill_host(): No need to check xlevel2

["Andreas Färber" <afaerber@suse.de>]

Am 24.11.2013 20:55, schrieb Eduardo Habkost:
> There's no need to check CPU xlevel2 before calling
> kvm_arch_get_supported_cpuid(s, 0xC0000001, 0, R_EDX), because:
> 
>  * The kernel won't return any entry for 0xC0000000 if host CPU vendor
>    is not Centaur (See kvm_dev_ioctl_get_supported_cpuid() on the kernel
>    code)
>  * Similarly, the kernel won't return any entry for 0xC0000001 if
>    CPUID[0xC0000000].EAX is < 0xC0000001
>  * kvm_arch_get_supported_cpuid() will return 0 if no entry is returned
>    by the kernel for the requested leaf
> 
> For similar reasons, we can simply set x86_cpu_def->xlevel2 directly
> instead of making it conditional, because it will be set to 0 CPU vendor
> is not Centaur.

"... if CPU vendor is not ..." I guess. :)

> 
> This will simplify the kvm_cpu_fill_host() code a little.
> 
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> ---
>  target-i386/cpu.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 41726f8..9731493 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -1176,13 +1176,11 @@ static void kvm_cpu_fill_host(x86_def_t *x86_cpu_def)
>      cpu_x86_fill_model_id(x86_cpu_def->model_id);
>  
>      /* Call Centaur's CPUID instruction. */
> -    eax = kvm_arch_get_supported_cpuid(s, 0xC0000000, 0, R_EAX);
> -    if (eax >= 0xC0000001) {
> -        /* Support VIA max extended level */
> -        x86_cpu_def->xlevel2 = eax;
> -        x86_cpu_def->features[FEAT_C000_0001_EDX] =
> -                kvm_arch_get_supported_cpuid(s, 0xC0000001, 0, R_EDX);
> -    }
> +    x86_cpu_def->xlevel2 =
> +        kvm_arch_get_supported_cpuid(s, 0xC0000000, 0, R_EAX);
> +    /* Support VIA max extended level */
> +    x86_cpu_def->features[FEAT_C000_0001_EDX] =
> +        kvm_arch_get_supported_cpuid(s, 0xC0000001, 0, R_EDX);
>  
>      /* Other KVM-specific feature fields: */
>      x86_cpu_def->features[FEAT_SVM] =

Sounds okay otherwise.

Andreas

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