Re: [Xen-devel] [PATCH] Nested VMX: Allow to set CR4.OSXSAVE if guest has xsave feature

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.08.13 at 04:26, Yang Zhang <yang.z.zhang@xxxxxxxxx> wrote:
>      case MSR_IA32_VMX_CR4_FIXED1:
> +        data = 0x267ff;
> +        /* Allow to set OSXSAVE if guest has xsave feature. */
> +        hvm_cpuid(0x1, &eax, &ebx, &ecx, &edx);
> +        if ( ecx & cpufeat_mask(X86_FEATURE_XSAVE) )
> +            data |= X86_CR4_OSXSAVE;
>          /* allow 0-settings except SMXE */
> -        data = 0x267ff & ~X86_CR4_SMXE;
> +        data &= ~X86_CR4_SMXE;

While fine with me in general, please take the opportunity and
eliminate the bogus literal 0x267ff (which will then also make it
unnecessary to explicitly remove X86_CR4_SMXE from the mask,
and will make obvious that the mask likely is missing
X86_CR4_FSGSBASE and X86_CR4_SMEP). I also wonder why
the OSXSAVE bit needs to be gated by a virtual CPUID check,
while all other bits don't: Is it possible that this code needs a
wider overhaul?

Jan


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