Re: [Xen-devel] [PATCH v2 3/3] x86/emul: Support CPUID faulting via a speculative MSR read

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.02.17 at 12:04, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 20/02/17 10:59, Jan Beulich wrote:
>>>>> On 20.02.17 at 11:28, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
>>> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
>>> @@ -5424,10 +5424,25 @@ x86_emulate(
>>>          break;
>>>  
>>>      case X86EMUL_OPC(0x0f, 0xa2): /* cpuid */
>>> +        msr_val = 0;
>>>          fail_if(ops->cpuid == NULL);
>>> +
>>> +        /* Speculatively read MSR_INTEL_MISC_FEATURES_ENABLES. */
>>> +        if ( ops->read_msr &&
>>> +             (rc = ops->read_msr(MSR_INTEL_MISC_FEATURES_ENABLES,
>>> +                                 &msr_val, ctxt)) == X86EMUL_EXCEPTION )
>>> +        {
>>> +            /* Not implemented.  Squash the exception and proceed 
>>> normally. */
>>> +            x86_emul_reset_event(ctxt);
>>> +            rc = X86EMUL_OKAY;
>>> +        }
>>> +        if ( rc != X86EMUL_OKAY )
>>> +            goto done;
>>> +
>>> +        generate_exception_if((msr_val & MSR_MISC_FEATURES_CPUID_FAULTING) 
>>> &&
>>> +                              !mode_ring0(), EXC_GP, 0); /* Faulting 
>>> active? */
>> Could you please move the mode_ring0() check up to bypass the
>> MSR read in the first place?
> 
> Ok.

With that
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel