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SubjectRe: [PATCH RFCv2 9/9] arm64: Support async page fault
On 2020-05-29 00:02, Gavin Shan wrote:
> Hi Paolo,
>
> On 5/28/20 8:48 PM, Paolo Bonzini wrote:
>> On 28/05/20 08:14, Gavin Shan wrote:
>>>> - for x86 we're also thinking of initiating the page fault from the
>>>> exception handler, rather than doing so from the hypervisor before
>>>> injecting the exception.  If ARM leads the way here, we would do our
>>>> best to share code when x86 does the same.
>>>
>>> Sorry, Paolo, I don't follow your idea here. Could you please provide
>>> more details?
>>
>> The idea is to inject stage2 page faults into the guest even before
>> the
>> host starts populates the page. The guest then invokes a hypercall,
>> telling the host to populate the page table and inject the 'page
>> ready'
>> event (interrupt) when it's done.
>>
>> For x86 the advantage is that the processor can take care of raising
>> the
>> stage2 page fault in the guest, so it's faster.
>>
> I think there might be too much overhead if the page can be populated
> quickly by host. For example, it's fast to populate the pages if swapin
> isn't involved.
>
> If I'm correct enough, it seems arm64 doesn't have similar mechanism,
> routing stage2 page fault to guest.

Indeed, this isn't a thing on arm64. Exception caused by a S2 fault are
always routed to EL2.

M.
--
Jazz is not dead. It just smells funny...

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