Re: [Xen-devel] [PATCH 04/18] PVH xen: add params to read_segment_register

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Fri, 07 Jun 2013 07:29:40 +0100
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> >>> On 07.06.13 at 03:43, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> >>> wrote:
> > On Thu, 06 Jun 2013 07:48:49 +0100
> > "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> > 
> >> >>> On 06.06.13 at 03:25, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> >> >>> wrote:
> >> > On Fri, 31 May 2013 11:00:12 +0100
> >> > "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> >> > 
........ 
> And anything we leave there should be optimized to hide latencies
> between dependent instructions (the worst example here likely is
> the CR2 read followed immediately by the intermediate register
> getting written to memory, even though the control register read
> could be done almost first thing in the handler).
> 
> One question though is why HVM code gets away without always
> filling those fields, but PVH code doesn't. Could you say a word
> on this?

Yeah, sure. The HVM IO instr emulation goes thru handle_mmio/handle_pio,
and I've not looked at them since the PVH goes thru emulate_privileged_op(),
which calls read_segment_register macro. The HVM functions do not call
the read_segment_register macro. 

Hope that helps.

Mukesh

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