Re: [PATCH v6 18/19] docs: hest: add new "etc/acpi_table_hest_addr" and update workflow

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Thu, 27 Feb 2025 17:00:56 +0100
Mauro Carvalho Chehab <mchehab+huawei@kernel.org> wrote:

> While the HEST layout didn't change, there are some internal
> changes related to how offsets are calculated and how memory error
> events are triggered.
> 
> Update specs to reflect such changes.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
One minor editorial suggestion. With that or similar tidy up,
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
>  docs/specs/acpi_hest_ghes.rst | 28 +++++++++++++++++-----------
>  1 file changed, 17 insertions(+), 11 deletions(-)
> 
> diff --git a/docs/specs/acpi_hest_ghes.rst b/docs/specs/acpi_hest_ghes.rst
> index c3e9f8d9a702..4311a9536b21 100644
> --- a/docs/specs/acpi_hest_ghes.rst
> +++ b/docs/specs/acpi_hest_ghes.rst
> @@ -89,12 +89,21 @@ Design Details
>      addresses in the "error_block_address" fields with a pointer to the
>      respective "Error Status Data Block" in the "etc/hardware_errors" blob.
>  
> -(8) QEMU defines a third and write-only fw_cfg blob which is called
> -    "etc/hardware_errors_addr". Through that blob, the firmware can send back
> -    the guest-side allocation addresses to QEMU. The "etc/hardware_errors_addr"
> -    blob contains a 8-byte entry. QEMU generates a single WRITE_POINTER command
> -    for the firmware. The firmware will write back the start address of
> -    "etc/hardware_errors" blob to the fw_cfg file "etc/hardware_errors_addr".
> +(8) QEMU defines a third and write-only fw_cfg blob to store the location
> +    where the error block offsets, read ack registers and CPER records are
> +    stored.
> +
> +    Up to QEMU 9.2, the location was at "etc/hardware_errors_addr", and
> +    contains a GPA for the beginning of "etc/hardware_errors".
> +
> +    Newer versions place the location at "etc/acpi_table_hest_addr",
> +    pointing to the GPA of the HEST table.
> +
> +    Through that such GPA values, the firmware can send back the guest-side
This confuses me.
 Via those GPA values...? (maybe?)

> +    allocation addresses to QEMU. They contain a 8-byte entry. QEMU generates
> +    a single WRITE_POINTER command for the firmware. The firmware will write
> +    back the start address of either "etc/hardware_errors" or HEST table at
> +    the corresponding fw_cfg file.
>  
>  (9) When QEMU gets a SIGBUS from the kernel, QEMU writes CPER into corresponding
>      "Error Status Data Block", guest memory, and then injects platform specific
> @@ -105,8 +114,5 @@ Design Details
>       kernel, on receiving notification, guest APEI driver could read the CPER error
>       and take appropriate action.
>  
> -(11) kvm_arch_on_sigbus_vcpu() uses source_id as index in "etc/hardware_errors" to
> -     find out "Error Status Data Block" entry corresponding to error source. So supported
> -     source_id values should be assigned here and not be changed afterwards to make sure
> -     that guest will write error into expected "Error Status Data Block" even if guest was
> -     migrated to a newer QEMU.
> +(11) kvm_arch_on_sigbus_vcpu() report RAS errors via a SEA notifications,
> +     when a SIGBUS event is triggered.