Re: [Xen-devel] [PATCH v15 17/21] x86/VPMU: Handle PMU interrupts for PV guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.11.14 at 15:39, <boris.ostrovsky@xxxxxxxxxx> wrote:

> On 11/25/2014 09:28 AM, Jan Beulich wrote:
>>
>>> +            else
>>> +            {
>>> +                struct segment_register seg;
>>> +
>>> +                hvm_get_segment_register(sampled, x86_seg_cs, &seg);
>>> +                r->cs = seg.sel;
>>> +                hvm_get_segment_register(sampled, x86_seg_ss, &seg);
>>> +                r->ss = seg.sel;
>>> +                if ( seg.attr.fields.dpl != 0 )
>>> +                    *flags |= PMU_SAMPLE_USER;
>> Is that how hardware treats it (CPL != 0 meaning user, rather
>> than CPL == 3)?
> 
> You mean how *software* (e.g. Linux kernel) treats it? If yes, then for 
> 32-bit user_mode() checks for (CS == 3) and for 64-bit it's !!(CS & 3).

No, I meant hardware. There CPL qualified PMU aspects, and it was
those I had in mind to use as reference here.

>> Maybe you should surface CPL instead of a
>> boolean flag?
> 
> Am I not already doing it by passing SS and CS to the guest?

No, neither SS.RPL nor CS.RPL formally represent CPL.

Jan


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