Re: [Xen-devel] [PATCH v2 4/6] x86/viridian: add warnings for unimplemented hypercalls and MSRs

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.03.17 at 18:08, <paul.durrant@xxxxxxxxxx> wrote:
> These warnings can be useful when Microsoft updates Windows.
> 
> In the past there have been several cases when Windows erroneously uses
> hypercalls and MSRs that should be gated on CPUID flags than Xen does
> not set. The usual symptom is a guest crash with little or no information
> in the hypervisor log. Adding these warnings at least gives a clue as to
> what might be happening in such cases.
> 
> Some versions of Windows do currently issue hypercalls that they should
> not, so this patch whitelists those to avoid the warnings as the lack
> of implementation is clearly proved not to be a problem to the guest.
> 
> The warnings are rate limited so a malicious guest cannot use them to
> as a DoS.
> 
> NOTE: Because the MSR warnings need to be gated on range checking the
>       MSR address this patch imports the up-to-date definitions of all
>       the viridian MSRs from the specification.
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

with one remark:

> @@ -552,6 +610,10 @@ int wrmsr_viridian_regs(uint32_t idx, uint64_t val)
>          break;
>  
>      default:
> +        if ( idx >= VIRIDIAN_MSR_MIN && idx <= VIRIDIAN_MSR_MAX )
> +            gprintk(XENLOG_WARNING, "write to unimplemented MSR %08x\n",
> +                    idx);

Mind if I shorten the string literal by one using %#x instead of
%08x (also on the read side) while committing?

Jan


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