linux-kernel - Re: [PATCH v6 13/18] KVM: arm64: Support SDEI_EVENT_{COMPLETE,COMPLETE_AND

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Date:   Mon, 2 May 2022 14:19:30 +0800
From:   Gavin Shan <gshan@...hat.com>
To:     Oliver Upton <oupton@...gle.com>
Cc:     kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        eauger@...hat.com, Jonathan.Cameron@...wei.com,
        vkuznets@...hat.com, will@...nel.org, shannon.zhaosl@...il.com,
        james.morse@....com, mark.rutland@....com, maz@...nel.org,
        pbonzini@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH v6 13/18] KVM: arm64: Support
 SDEI_EVENT_{COMPLETE,COMPLETE_AND_RESUME} hypercall

Hi Oliver,

On 5/1/22 2:50 PM, Oliver Upton wrote:
> On Sun, Apr 03, 2022 at 11:39:06PM +0800, Gavin Shan wrote:
>> This supports SDEI_EVENT_{COMPLETE, COMPLETE_AND_RESUME} hypercall.
>> They are used by guest to notify the completion of event in its
>> handler. The previously interrupted or preempted context is restored
>> like below.
>>
>>     * x0 - x17, PC and PState are restored to what values we had in
>>       the interrupted or preempted context.
>>
>>     * If it's SDEI_EVENT_COMPLETE_AND_RESUME hypercall, IRQ exception
>>       is injected.
> 
> I don't think that's how COMPLETE_AND_RESUME works. The caller specifies an
> address at which it would like to begin execution within the client
> exception level.
> 
> SDEI spec suggests this behaves like a synchronous exception. DEN 0054C
> 5.2.2 'Event Resume Context' speaks more about how it is supposed to
> work.
> 

It's actually the linux convention. If the event handler, which was
specified in previous hypercall to EVENT_REGISTER, returns success,
the (linux) client calls into COMPLETE_AND_RESUME and the resume
address is specified with FIQ vector offset. More details can be
found from arch/arm64/kernel::sdei.c::do_sdei_event().

Thanks,
Gavin