linux-kernel - Re: [PATCH v8 06/13] acpi/ghes: add support for generic error injection via QAPI

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Message-ID: <20240911152132.65a7a219@imammedo.users.ipa.redhat.com>
Date: Wed, 11 Sep 2024 15:21:32 +0200
From: Igor Mammedov <imammedo@...hat.com>
To: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>, Shiju Jose
 <shiju.jose@...wei.com>, "Michael S. Tsirkin" <mst@...hat.com>, Ani Sinha
 <anisinha@...hat.com>, Dongjiu Geng <gengdongjiu1@...il.com>,
 linux-kernel@...r.kernel.org, qemu-arm@...gnu.org, qemu-devel@...gnu.org
Subject: Re: [PATCH v8 06/13] acpi/ghes: add support for generic error
 injection via QAPI

On Sun, 25 Aug 2024 05:29:23 +0200
Mauro Carvalho Chehab <mchehab+huawei@...nel.org> wrote:

> Em Mon, 19 Aug 2024 14:51:36 +0200
> Igor Mammedov <imammedo@...hat.com> escreveu:
> 
> > > +        read_ack = 1;
> > > +        cpu_physical_memory_write(read_ack_start_addr,
> > > +                                  &read_ack, (uint64_t));    
> > we don't do this for SEV so, why are you setting it to 1 here?  
> 
> According with:
> https://uefi.org/specs/ACPI/6.5/18_Platform_Error_Interfaces.html#generic-hardware-error-source-version-2-ghesv2-type-10
> 
>    "These are the steps the OS must take once detecting an error from a particular GHESv2 error source:
> 
>     OSPM detects error (via interrupt/exception or polling the block status)
> 
>     OSPM copies the error status block
> 
>     OSPM clears the block status field of the error status block
> 
>     OSPM acknowledges the error via Read Ack register. For example:
> 
>         OSPM reads the Read Ack register –> X
> 
>         OSPM writes –> (( X & ReadAckPreserve) | ReadAckWrite)"
> 
> 
> So, basically the guest OS takes some time to detect that an error
> is raised. When it detects, it needs to mark that the error was
> handled.

what you are doing here by setting read_ack = 1,
is making ack on behalf of OSPM when OSPM haven't handled existing error yet.

Essentially making HW/FW do the job of OSPM. That looks wrong to me.
From HW/FW side read_ack register should be thought as read-only.

> 
> IMO, this is needed, independently of the notification mechanism.
> 
> Regards,
> Mauro
>