Re: [Qemu-devel] [PATCH] i386: correct cpu_x86_cpuid(0xd)

[Eduardo Habkost]

On Fri, Sep 28, 2018 at 12:43:19PM +0200, Sebastian Andrzej Siewior wrote:
> Intel SDM says for CPUID function 0DH, sub-function 0:
> 
> | • ECX enumerates the size (in bytes) required by the XSAVE instruction for 
> an
> |   XSAVE area containing all the user state components supported by this
> |   processor.
> | • EBX enumerates the size (in bytes) required by the XSAVE instruction for 
> an
> |   XSAVE area containing all the user state components corresponding to bits
> |   currently set in XCR0.
> 
> Signed-off-by: Sebastian Andrzej Siewior <address@hidden>
> ---
>  target/i386/cpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index f24295e6e4bb7..00c18444c0bac 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -4178,7 +4178,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> uint32_t count,
>              *ecx = xsave_area_size(x86_cpu_xsave_components(cpu));
>              *eax = env->features[FEAT_XSAVE_COMP_LO];
>              *edx = env->features[FEAT_XSAVE_COMP_HI];
> -            *ebx = *ecx;
> +            *ebx = xsave_area_size(env->xcr0);

Reviewed-by: Eduardo Habkost <address@hidden>

For reference, KVM isn't affected by this bug because KVM kernel code updates
CPUID data at runtime, at:

int kvm_update_cpuid(struct kvm_vcpu *vcpu)
{
        [...]
        best = kvm_find_cpuid_entry(vcpu, 0xD, 0);
        if (!best) {
                [...]
        } else {
                [...]
                best->ebx = xstate_required_size(vcpu->arch.xcr0, false);
        }
        [...]
}


>          } else if (count == 1) {
>              *eax = env->features[FEAT_XSAVE];
>          } else if (count < ARRAY_SIZE(x86_ext_save_areas)) {
> -- 
> 2.19.0
> 

-- 
Eduardo