Re: [Qemu-devel] [PATCH] target-i386: fix losing XCR0 processor state component bits

[Paolo Bonzini <bonzini@gnu.org>]

On 28/09/2016 07:31, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
> 
> Commit 96193c22a "target-i386: Move xsave component mask to features array"
> leverages features array to handle XCR0 processor state component bits, 
> however, it introduces a regression:
> 
> warning: host doesn't support requested feature: CPUID.0DH:EAX [bit 0]
> warning: host doesn't support requested feature: CPUID.0DH:EAX [bit 1]
> warning: host doesn't support requested feature: CPUID.0DH:EAX [bit 2]
> 
> My desktop doesn't have enough advance features, so just X87,SSE,AVX 
> warnings are splat when I boot a guest.
> 
> The get migratable flags logic in x86_cpu_filter_features() path will 
> filter out the feature flags which are unsupported and unmigratable. 
> However, the bits of XCR0 processor state component featureword don't 
> have feat_names, and some features like SSE/AVX etc have feat_names in 
> CPUID.01H:EDX, CPUID.01H:ECX, so they are treated as unsupported.
> 
> This patch fix it by don't filter out XCR0 processor state components 
> bits though they don't have feat_names just as before commit 96193c22ab3.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
>  target-i386/cpu.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index ad09246..9d24eff 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -2156,6 +2156,10 @@ static uint32_t x86_cpu_get_supported_feature_word(FeatureWord w,
>          r = kvm_arch_get_supported_cpuid(kvm_state, wi->cpuid_eax,
>                                                      wi->cpuid_ecx,
>                                                      wi->cpuid_reg);
> +        if ((w == FEAT_XSAVE_COMP_LO) ||
> +            (w == FEAT_XSAVE_COMP_HI)) {
> +            return r;
> +        }
>      } else if (tcg_enabled()) {
>          r = wi->tcg_features;
>      } else {
> 

I think the right place to add the test is x86_cpu_get_migratable_flags.

Paolo