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

On 11/27/2014 03:59 AM, Jan Beulich wrote:
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?

Yes, I think it may be better. Let the caller sort out how to interpret it.


Am I not already doing it by passing SS and CS to the guest?
No, neither SS.RPL nor CS.RPL formally represent CPL.


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