Re: [Qemu-devel] [PATCH 14/14] target-i386: Enable XCR0 features for user-mode

[Paolo Bonzini]

On 09/07/2015 10:17, Richard Henderson wrote:
> +
> +    /* ??? This variable is somewhat silly.  Methinks KVM should be
> +       using XCR0 to store into the XSTATE_BV field.  Either that or
> +       there's more missing information, e.g. the AVX bits.  */
> +    env->xstate_bv = XSTATE_FP;
> +    if (env->features[FEAT_1_EDX] & CPUID_SSE) {
> +        env->xstate_bv |= XSTATE_SSE;
> +    }
> +    if (env->features[FEAT_7_0_EBX] & CPUID_7_0_EBX_MPX) {
> +        env->xstate_bv |= XSTATE_BNDREGS | XSTATE_BNDCSR;
> +    }

xstate_bv != xcr0 if the kernel is using XSAVEOPT and some of the values
were in the initial state.  Legacy state is never optimized, hence the
value of env->xstate_bv after reset.  So I think this hunk is wrong,
while the other is correct.

Paolo