Re: [Xen-devel] [PATCH v5 7/9] x86/paravirt: Add paravirt_{read, write}_msr

[Andy Lutomirski <luto@xxxxxxxxxxxxxx>]

On Mon, Apr 4, 2016 at 9:33 AM, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> On 02/04/16 15:01, Andy Lutomirski wrote:
>> This adds paravirt hooks for unsafe MSR access.  On native, they
>> call native_{read,write}_msr.  On Xen, they use
>> xen_{read,write}_msr_safe.
>>
>> Nothing uses them yet for ease of bisection.  The next patch will
>> use them in rdmsrl, wrmsrl, etc.
>>
>> I intentionally didn't make them warn on #GP on Xen.  I think that
>> should be done separately by the Xen maintainers.
> ...
>> --- a/arch/x86/xen/enlighten.c
>> +++ b/arch/x86/xen/enlighten.c
>
> Reviewed-by: David Vrabel <david.vrabel@xxxxxxxxxx>
>
>> @@ -1092,6 +1092,26 @@ static int xen_write_msr_safe(unsigned int msr, 
>> unsigned low, unsigned high)
>>       return ret;
>>  }
>>
>> +static u64 xen_read_msr(unsigned int msr)
>> +{
>> +     /*
>> +      * This will silently swallow a #GP from RDMSR.  It may be worth
>> +      * changing that.
>
> This probably isn't important.
>

It might be nice to do a WARN_ON_ONCE like this series does for the
native case to help shake out latent bugs.

--Andy

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