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Re: [PATCH RESEND v10 2/2] x86/xen: Allow per-domain usage of hardware virtualized APIC
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Jane Malalane <Jane.Malalane@xxxxxxxxxx>
- Date: Mon, 11 Jul 2022 08:00:29 +0000
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- Thread-topic: [PATCH RESEND v10 2/2] x86/xen: Allow per-domain usage of hardware virtualized APIC
On 30/06/2022 07:03, Jan Beulich wrote:
> 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.
>
> JanHello Jan,
In the previous email, I was referring to this discussion about the
commit message. I haven't sent out a v11 because there was no change
other than this one suggested. What I said earlier was that I thought
the "Having all APIC interaction exit to Xen for emulation is slow..."
paragraph provided context for what I say after but I am happy to remove it.
Thanks,
Jane.
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