linux-kernel - Re: [PATCH v5 6/7] acpi/ghes: add support for generic error injection via QAPI

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Message-ID: <20240807094750.6414fb2f@foz.lan>
Date: Wed, 7 Aug 2024 09:47:50 +0200
From: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To: Igor Mammedov <imammedo@...hat.com>, Jonathan Cameron
 <Jonathan.Cameron@...wei.com>
Cc: 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 v5 6/7] acpi/ghes: add support for generic error
 injection via QAPI

Em Tue, 6 Aug 2024 16:31:13 +0200
Igor Mammedov <imammedo@...hat.com> escreveu:

> PS:
> looking at the code, ACPI_GHES_MAX_RAW_DATA_LENGTH is 1K
> and it is the total size of a error block for a error source.
> 
> However acpi_hest_ghes.rst (3) says it should be 4K,
> am I mistaken?

Maybe Jonathan knows better, but I guess the 1K was just some
arbitrary limit to prevent a too big CPER. The 4K limit described
at acpi_hest_ghes.rst could be just some limit to cope with
the current bios implementation, but I didn't check myself how
this is implemented there. 

I was unable to find any limit at the specs. Yet, if you look at:

https://uefi.org/specs/UEFI/2.10/Apx_N_Common_Platform_Error_Record.html#arm-processor-error-section

The processor Error Information Structure, starting at offset
40, can go up to 255*32, meaning an offset of 8200, which is
bigger than 4K.

Going further, processor context can have up to 65535 (spec
actually says 65536, but that sounds a typo, as the size is
stored on an uint16_t), containing multiple register values
there (the spec calls its length as "P").

So, the CPER record could, in theory, have:
	8200 + (65535 * P) + sizeof(vendor-specicific-info)

The CPER length is stored in Section Length record, which is
uint32_t.

So, I'd say that the GHES record can theoretically be a lot
bigger than 4K.	

Thanks,
Mauro