linux-kernel - Re: [PATCH 1/2] platform/x86/amd: Introduce AMD Address Translation Library

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Date:   Mon, 7 Aug 2023 22:17:33 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Yazen Ghannam <yazen.ghannam@....com>, bp@...en8.de,
        linux-edac@...r.kernel.org, hdegoede@...hat.com,
        markgross@...nel.org, platform-driver-x86@...r.kernel.org,
        "Luck, Tony" <tony.luck@...el.com>
Cc:     linux-kernel@...r.kernel.org, avadhut.naik@....com
Subject: Re: [PATCH 1/2] platform/x86/amd: Introduce AMD Address Translation
 Library



On 8/7/2023 3:44 PM, Yazen Ghannam wrote:
> On 8/2/2023 2:55 PM, Yazen Ghannam wrote:
>> AMD Zen-based systems report memory errors through Machine Check banks
>> representing Unified Memory Controllers (UMCs). The address value
>> reported for DRAM ECC errors is a "normalized address" that is relative
>> to the UMC. This normalized address must be converted to a system
>> physical address to be usable by the OS.
>>
>> Support for this address translation was introduced to the MCA subsystem
>> with Zen1 systems. The code was later moved to the AMD64 EDAC module,
>> since this was the only user of the code at the time.
>>
>> However, there are uses for this translation outside of EDAC. The system
>> physical address can be used in MCA for preemptive page offlining as done
>> in some MCA notifier functions. Also, this translation is needed as the
>> basis of similar functionality needed for some CXL configurations on AMD
>> systems.
>>
>> Introduce a common address translation library that can be used for
>> multiple subsystems including MCA, EDAC, and CXL.
>>
>> Include support for UMC normalized to system physical address
>> translation for current CPU systems.
>>
>> Future development to include:
>> - DF4.5 Non-power-of-2 interleaving modes.
>> - Heterogeneous CPU+GPU system support.
>> - CXL translation support.
>> - Caching of common intermediate values and results.
>> - Leverage UEFI PRM methods as alternate backends to existing native
>>    code.
>>
>> Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
>> ---
>>   MAINTAINERS                                |   7 +
>>   drivers/platform/x86/amd/Kconfig           |   1 +
>>   drivers/platform/x86/amd/Makefile          |   1 +
>>   drivers/platform/x86/amd/atl/Kconfig       |  20 +
>>   drivers/platform/x86/amd/atl/Makefile      |  18 +
>>   drivers/platform/x86/amd/atl/access.c      | 107 ++++
>>   drivers/platform/x86/amd/atl/core.c        | 212 +++++++
>>   drivers/platform/x86/amd/atl/dehash.c      | 459 ++++++++++++++
>>   drivers/platform/x86/amd/atl/denormalize.c | 644 ++++++++++++++++++++
>>   drivers/platform/x86/amd/atl/internal.h    | 307 ++++++++++
>>   drivers/platform/x86/amd/atl/map.c         | 659 +++++++++++++++++++++
>>   drivers/platform/x86/amd/atl/reg_fields.h  | 603 +++++++++++++++++++
>>   drivers/platform/x86/amd/atl/system.c      | 282 +++++++++
>>   drivers/platform/x86/amd/atl/umc.c         |  53 ++
>>   include/linux/amd-atl.h                    |  18 +
>>
> 
> Hi all,
> 
> I'd like to get feedback on the most appropriate place for this code.
> 
> I want to move this out of EDAC, since it's not really an EDAC feature. 
> And it needs to be used by subsystems other than EDAC.
> 
> I thought x86 Platform Drivers, because the code is very 
> platform-specific. And there are already some AMD platform drivers. But 
> there isn't any platform control or management for this translation. 
> It's just reading registers and calculating values. So it's not really a 
> "platform driver" in the sense that it manages platform-specific behavior.
> 
> Another option is for this code to be in arch/x86/ras/. But I would like 
> the option for this code to be built as a module, at least for debug and 
> development. And I don't know that modules, nor platform-specific code, 
> should be in arch/.
> 
> Currently, I think this could go in drivers/ras/. This address 
> translation is needed for RAS use cases, so making it a part of "RAS 
> Infrastructure" may make the most sense.
> 
> Boris, Tony, (and others) what do you think?

Given it's 'library code' to be used by a bunch of things and also want 
to be able to use a module, what about putting it in lib/?  There's 
plenty of library code there as tristate.