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Re: [PATCH RESEND v10 2/2] x86/xen: Allow per-domain usage of hardware virtualized APIC
- To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 30 Jun 2022 08:03:10 +0200
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- Cc: Wei Liu <wl@xxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Nick Rosbrook <rosbrookn@xxxxxxxxx>, "Gross, Jurgen" <jgross@xxxxxxxx>, Christian Lindig <christian.lindig@xxxxxxxxxx>, David Scott <dave@xxxxxxxxxx>, "Cooper, Andrew" <andrew.cooper3@xxxxxxxxxx>, Pau Monné, Roger <roger.pau@xxxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>, Jane Malalane <jane.malalane@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 30 Jun 2022 06:03:28 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.06.2022 05:25, Tian, Kevin wrote:
>> From: Jane Malalane <jane.malalane@xxxxxxxxxx>
>> Sent: Wednesday, June 29, 2022 9:56 PM
>>
>> Introduce a new per-domain creation x86 specific flag to
>> select whether hardware assisted virtualization should be used for
>> x{2}APIC.
>>
>> A per-domain option is added to xl in order to select the usage of
>> x{2}APIC hardware assisted virtualization, as well as a global
>> configuration option.
>>
>> Having all APIC interaction exit to Xen for emulation is slow and can
>> induce much overhead. Hardware can speed up x{2}APIC by decoding the
>> APIC access and providing a VM exit with a more specific exit reason
>> than a regular EPT fault or by altogether avoiding a VM exit.
>
> Above is obvious and could be removed.
>
> I think the key is just the next paragraph for why we
> want this per-domain control.
Indeed, but the paragraph above sets the context. It might be possible
to shorten it, but ...
> Apart from that:
>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
>
>>
>> On the other hand, being able to disable x{2}APIC hardware assisted
>> virtualization can be useful for testing and debugging purposes.
... I think it is desirable for this sentence to start with "Otoh" or
alike.
Jan
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