Re: [Xen-devel] [PATCH v3 2/2] x86/xstate: Make errors in xstate calculations more obvious by crashing the domain

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.07.18 at 13:44, <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/xstate.c
> +++ b/xen/arch/x86/xstate.c
> @@ -707,12 +707,32 @@ int handle_xsetbv(u32 index, u64 new_bv)
>      if ( index != XCR_XFEATURE_ENABLED_MASK )
>          return -EOPNOTSUPP;
>  
> -    if ( (new_bv & ~xcr0_max) ||
> -         (new_bv & ~xfeature_mask) || !valid_xcr0(new_bv) )
> +    /*
> +     * The CPUID logic shouldn't be able to hand out an XCR0 exceeding Xen's
> +     * maximum features, but keep the check for robustness.
> +     */
> +    if ( unlikely(xcr0_max & ~xfeature_mask) )
> +    {
> +        gprintk(XENLOG_ERR,
> +                "xcr0_max %016" PRIx64 " exceeds hardware max %016" PRIx64 
> "\n",
> +                new_bv, xfeature_mask);

I've only noticed this while doing the 4.8 backport: I don't think you've
meant to log new_bv here, rather than xcr0_max.

Jan



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