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Re: [Xen-devel] [PATCH] x86/altp2m: Allow setting the #VE info page for an arbitrary VCPU


  • To: Jan Beulich <JBeulich@xxxxxxxx>, Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Wed, 1 Aug 2018 09:38:19 +0100
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  • Cc: Sergej Proskurin <proskurin@xxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Adrian Pop <apop@xxxxxxxxxxxxxxx>
  • Delivery-date: Wed, 01 Aug 2018 08:38:30 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 01/08/2018 09:23, Jan Beulich wrote:
>>>> On 31.07.18 at 19:19, <tamas@xxxxxxxxxxxxx> wrote:
>> On Tue, Jul 31, 2018 at 5:53 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>>> On 25.07.18 at 13:49, <apop@xxxxxxxxxxxxxxx> wrote:
>>>> -        vcpu_altp2m(curr).veinfo_gfn = _gfn(a.u.enable_notify.gfn);
>>>> -        altp2m_vcpu_update_vmfunc_ve(curr);
>>>> +        vcpu_altp2m(v).veinfo_gfn = _gfn(a.u.enable_notify.gfn);
>>>> +        altp2m_vcpu_update_vmfunc_ve(v);
>>> I'd like you to outline in the description how you mean an external
>>> agent to coordinate the use of this GFN with the guest (and in
>>> particular without in-guest agent).
>> Using #VE without an in-guest agent isn't really possible so this is
>> really just about designating the page from dom0 instead of doing it
>> with the in-guest agent. Something has to be present in the guest to
>> handle the new interrupts coming from #VE after all.
> Not necessarily - the exception could also be intercepted, and the
> external agent be informed, with it taking appropriate action.
>
> Anyway - if such a dependency continues to exist, I think it would
> be desirable to mention it in the description.

Any setup which intercepts #VE defeats the entire purpose of using #VE
in the first place.

We'll eventually have to cope with this situation because its not one we
can architecturally rule out (especially with nested virt in the mix),
but intercepting #VE is not something we should make available as a
user-available option.

~Andrew

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