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From: =?windows-1252?Q?Roger_Pau_Monn=E9?= <roger.pau@citrix.com>
Subject: Re: [PATCH v3 07/32] xen/x86: fix arch_set_info_guest
 for HVM guests
Date: Mon, 27 Jul 2015 13:55:32 +0200
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To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Ian Campbell <ian.campbell@citrix.com>, Andrew Cooper <andrew.cooper3@citrix.com>, David Vrabel <david.vrabel@citrix.com>, Jan Beulich <JBeulich@suse.com>, xen-devel@lists.xenproject.org, Boris Ostrovsky <boris.ostrovsky@oracle.com>
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El 24/07/15 a les 19.36, Konrad Rzeszutek Wilk ha escrit:
> On Fri, Jul 24, 2015 at 06:54:09PM +0200, Roger Pau Monn=E9 wrote:
>> I have the feeling that we are over engineering this interface. IMHO we
>> should only allow the user to set the control registers, efer (on amd64)
>> and the GP registers. Segment selectors would be set by Xen to point to
>> a flat segment suitable for the mode the guest has selected. I think
>> that should be enough to get the guest OS into it's entry point, and
>> then it can do whatever it wants.
> =

> If you are doing that why not use the old interface?

Because the current structure contains quite a lot of PV fields, like
the failsafe_callback, the GDT... Also the old structure is limited in a
way that you can only use the x86-<bitness> format if your kernel is
compiled with <bitness>, and we want to allow the vCPU to start in any
mode, regardless of the mode the kernel is compiled with.

>>
>> If that's not suitable, then my second option would be to allow the
>> guest to set the base, limit and AR bytes of the selectors, but not load
>> a GDT.
> =

> They should be able to do any of those operations as a normal HVM
> guest I would think?

Yes, hence I would like to limit setting anything that's not essential
to boot.