Re: [PATCH] x86/msr: don't inject #GP when trying to read FEATURE_CONTROL

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.11.2020 11:46, Roger Pau Monne wrote:
> Windows 10 will triple fault if #GP is injected when attempting to
> read the FEATURE_CONTROL MSR on Intel or compatible hardware. Fix this
> by injecting a #GP only when the vendor doesn't support the MSR, even
> if there are no features to expose.
> 
> Fixes: 39ab598c50a2 ('x86/pv: allow reading FEATURE_CONTROL MSR')
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

In principle
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

However, iirc it was Andrew who had suggested the conditional you
now replace, so I'd like to wait for him to voice a view.

> --- a/xen/arch/x86/msr.c
> +++ b/xen/arch/x86/msr.c
> @@ -176,7 +176,7 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t 
> *val)
>      switch ( msr )
>      {
>      case MSR_IA32_FEATURE_CONTROL:
> -        if ( !cp->basic.vmx && !vmce_has_lmce(v) )
> +        if ( !(cp->x86_vendor & (X86_VENDOR_INTEL | X86_VENDOR_CENTAUR)) )

What about Shanghai? init_shanghai() calling init_intel_cacheinfo()
suggests to me it's at least as Intel-like as Centaur/VIA.

Jan