Re: [PATCH v2] target-i386: fix losing XCR0 processor state component bits

[Eduardo Habkost <ehabkost@redhat.com>]

On Wed, Sep 28, 2016 at 04:36:14PM +0800, 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>
> ---
> v1 -> v2: 
>  * move the check to x86_cpu_get_migratable_flags()
> 
>  target-i386/cpu.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 333309b..cc929ca 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -602,7 +602,10 @@ static uint32_t x86_cpu_get_migratable_flags(FeatureWord w)
>          uint32_t f = 1U << i;
>          /* If the feature name is unknown, it is not supported by QEMU yet */
>          if (!wi->feat_names[i]) {
> -            continue;
> +            if (w != FEAT_XSAVE_COMP_LO &&
> +                w != FEAT_XSAVE_COMP_HI) {
> +                continue;
> +            }

We still need to report unknown xstate components as unmigratable
(otherwise -cpu host will enable them automatically). See the fix
I submitted:
  [PATCH] target-i386: Report known CPUID[EAX=0xD,ECX=0]:EAX bits as migratable

-- 
Eduardo