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Reply-To: Gavin Shan <gshan@redhat.com>
Subject: Re: [PATCH v6 13/18] KVM: arm64: Support
 SDEI_EVENT_{COMPLETE,COMPLETE_AND_RESUME} hypercall
To:     Oliver Upton <oupton@google.com>
Cc:     kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
        eauger@redhat.com, Jonathan.Cameron@huawei.com,
        vkuznets@redhat.com, will@kernel.org, shannon.zhaosl@gmail.com,
        james.morse@arm.com, mark.rutland@arm.com, maz@kernel.org,
        pbonzini@redhat.com, shan.gavin@gmail.com
References: <20220403153911.12332-1-gshan@redhat.com>
 <20220403153911.12332-14-gshan@redhat.com> <Ym4tzRL0iMxyumJe@google.com>
From:   Gavin Shan <gshan@redhat.com>
Message-ID: <ba094956-2e58-4913-527a-af79475ee949@redhat.com>
Date:   Mon, 2 May 2022 14:19:30 +0800
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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