linux-kernel - Re: [PATCH] kvm: pass the virtual SEI syndrome to guest OS

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Date:   Tue, 28 Mar 2017 11:48:08 +0100
From:   James Morse <james.morse@....com>
To:     Christoffer Dall <cdall@...aro.org>
CC:     gengdongjiu <gengdongjiu@...wei.com>, xiexiuqi@...wei.com,
        Marc Zyngier <marc.zyngier@....com>, catalin.marinas@....com,
        will.deacon@....com, christoffer.dall@...aro.org,
        rkrcmar@...hat.com, suzuki.poulose@....com, andre.przywara@....com,
        mark.rutland@....com, vladimir.murzin@....com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        wangxiongfeng2@...wei.com, wuquanming@...wei.com,
        huangshaoyu@...wei.com, Achin Gupta <Achin.Gupta@....com>,
        Leif.Lindholm@...aro.com
Subject: Re: [PATCH] kvm: pass the virtual SEI syndrome to guest OS

Hi Christoffer,

(CC: Leif and Achin who know more about how UEFI fits into this picture)

On 21/03/17 19:39, Christoffer Dall wrote:
> On Tue, Mar 21, 2017 at 07:11:44PM +0000, James Morse wrote:
>> On 21/03/17 11:34, Christoffer Dall wrote:
>>> On Tue, Mar 21, 2017 at 02:32:29PM +0800, gengdongjiu wrote:
>>>> On 2017/3/20 23:08, James Morse wrote:
>>>>>>>> On 20/03/17 07:55, Dongjiu Geng wrote:
>>>>>>>>> In the RAS implementation, hardware pass the virtual SEI
>>>>>>>>> syndrome information through the VSESR_EL2, so set the virtual
>>>>>>>>> SEI syndrome using physical SEI syndrome el2_elr to pass to
>>>>>>>>> the guest OS
>>>>>
>>>>> How does this work with firmware first?
>>>>
>>>> I explained it in previous mail about the work flow.
>>>
>>> When delivering and reporting SEIs to the VM, should this happen
>>> directly to the OS running in the VM, or to the guest firmware (e.g.
>>> UEFI) running in the VM as well?
>>
>> 'firmware first' is the ACPI specs name for x86's BIOS or management-mode
>> handling the error. On arm64 we have multiple things called firmware, so the
>> name might be more confusing than helpful.
>>
>> As far as I understand it, firmware here refers to the secure-world and EL3.
>> Something like ATF can use SCR_EL3.EA to claim SErrors and external aborts,
>> routing them to EL3 where secure platform specific firmware generates CPER records.
>> For a guest, Qemu takes the role of this EL3-firmware.
>>
> Thanks for the clarification.  So UEFI in the VM would not be involved
> in this at all?

On the host, part of UEFI is involved to generate the CPER records.
In a guest?, I don't know.
Qemu could generate the records, or drive some other component to do it.

Leif and Achin are the people with the UEFI/bigger picture.


> My confusion here comes from not thinking about QEMU or KVM as firmware,
> but as the machine, so it would be sort of like the functionality is
> baked into hardware rather than firmware.
> 
> Note that to the VM, the environment will look like hardware without EL3
> and without a secure world, so any software assuming there's something
> 'hidden' behind the available non-secure modes must not decide to
> disable features if discovering the lack of a secure world.


Thanks,

James