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Re: [PATCH] x86/msr: don't inject #GP when trying to read FEATURE_CONTROL
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Tue, 29 Dec 2020 17:47:20 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 29 Dec 2020 16:48:06 +0000
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On Fri, Nov 27, 2020 at 11:56:25AM +0100, Jan Beulich wrote:
> 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.
Right, and it also has VMX AFAICT. I'm not sure whether we could also
gate on the presence of VMX and LMCE on the physical CPU. I will send
and updated version with Shanghai added and will keep your Ack.
Thanks, Roger.
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