Re: [Xen-devel] PV Autotranslate guests (are they used at all?)

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> On Dec 8, 2016, at 4:37 AM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> 
> Hello,
> 
> While digging around, it looks like there is some major bitrot of the PV
> autotranslate code.
> 
> When constructing an autotranslate domain, tools/libxc/xc_dom_x86.c:
> x86_shadow() sets refcount | translate on the domain.
> 
> The combination of translate != external was excluded by c/s
> 92942fd3d469, which means that PV autotranslate guests can't boot on Xen
> 4.7 or later.
> 
> The shadow emulation code for PV guests (which gets used one way or
> another if any of refcount|translate|external are set) always sets up
> emulation in the same mode as Xen's %cs.  It appears to have had this
> behaviour since its introduction in c/s 1daf5e293b, and presumably means
> that noone has tried running a 32bit autotranslate guest on 64bit Xen in
> anger.
> 
> Does anyone use PV autotranslate guests at all?  I don't believe I have
> never come across one.

I used them for my PhD thesis that I finished up in 2006 — that’s probably why 
the code is there in the first place.  And the only reason I used PV guests 
instead of HVM guests is that when I started my work in 2004 HVM guests didn’t 
exist.  If execution replay is ever implemented again, it would probably be 
with PVH guests.

So no objection from me either.

 -George

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