Re: [Xen-devel] [PATCH 2/3] x86/boot: Cache cpu_has_hypervisor very early on boot

[Jan Beulich <jbeulich@xxxxxxxx>]

On 01.11.2019 21:25, Andrew Cooper wrote:
> --- a/xen/arch/x86/boot/head.S
> +++ b/xen/arch/x86/boot/head.S
> @@ -630,6 +630,10 @@ trampoline_setup:
>  
>  1:
>          /* Interrogate CPU extended features via CPUID. */
> +        mov     $1, %eax
> +        cpuid
> +        mov     %ecx, sym_fs(boot_cpu_data) + 
> CPUINFO_FEATURE_OFFSET(X86_FEATURE_HYPERVISOR)

I understand the ECX output is all we need right now. But wouldn't
it be better to then store EDX as well (and similarly ECX of
0x80000001 output)?

Also, along the lines of a question back to Sergey on his
standalone patch, wouldn't it be better to take the opportunity
and check here that CPUID leaf 1 is actually valid?

Of course the question on the (intended) effect of
"cpuid=no-hypervisor" also remains. As said before, I think this
should be honored by all of our code that possibly can (i.e. at
least everything following command line parsing).

Jan

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