Re: [Xen-devel] [PATCH v2] xen: handle paged gfn in wrmsr_hypervisor_regs

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 03/05/2013 14:58, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

>>>> On 03.05.13 at 14:57, Olaf Hering <olaf@xxxxxxxxx> wrote:
>> @@ -1682,14 +1682,25 @@ static int svm_msr_write_intercept(unsig
>>          if ( wrmsr_viridian_regs(msr, msr_content) )
>>              break;
>>  
>> -        wrmsr_hypervisor_regs(msr, msr_content);
>> +        ret = wrmsr_hypervisor_regs(msr, msr_content);
>> +        switch ( ret )
>> +        {
>> +            case -EAGAIN:
>> +                result = X86EMUL_RETRY;
>> +                break;
>> +            case 0:
>> +                result = X86EMUL_UNHANDLEABLE;
>> +                break;
>> +            default:
>> +                break;
> 
> As you had already noticed the hard way - case 0 and default of
> course need to be switched (0 -> okay, anything else ->
> unhandleable).

No!

Actually anything other than -EAGAIN should be handled here as 'okay'. In
fact the return codes from wrmsr_hypervisor_regs are going to be a bit of a
mess if we're not careful.

I suggest the following return codes:
 0: not handled
 1: handled
 -EINVAL: error during handling
 -EAGAIN: retry

The HVM callers should then handle as follows:
 -EAGAIN: rc = X86EMUL_RETRY
 -EINVAL: goto gp_fault
 0: try other msr handlers (if any)
 1: we're done, return X86EMUL_OKAY

Does that make sense?

 -- Keir

> Jan
> 
> 
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