linux-kernel - Re: [PATCH v3 3/8] hwmon: (k10temp) Check return value of amd_smn

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Message-ID: <f5b9aa86-f8a2-49ac-bc7c-7121a1bdb342@amd.com>
Date: Wed, 5 Jun 2024 13:41:36 -0400
From: Yazen Ghannam <yazen.ghannam@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: yazen.ghannam@....com, Guenter Roeck <linux@...ck-us.net>,
 x86@...nel.org, Mario Limonciello <mario.limonciello@....com>,
 linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hwmon@...r.kernel.org
Subject: Re: [PATCH v3 3/8] hwmon: (k10temp) Check return value of
 amd_smn_read()

On 6/5/24 12:45 PM, Borislav Petkov wrote:
> On Wed, Jun 05, 2024 at 12:30:35PM -0400, Yazen Ghannam wrote:
>> "It fixes a problem like ... a hardware quirk ..."
> 
> I'm pretty sure that means a patch which sets a magic bit in some MSR or
> does something else to make the hardware work again. Errata fix and some
> other hackery we get to do from time to time. Or my favourite - fix
> a BIOS f*ckup.
>

Yeah, makes sense. I agree.

>> Most systems will return 0 for SMN addresses that are not accessible.
>> This is in line with AMD convention that unavailable registers are
>> Read-as-Zero/Writes-Ignored.
>>
>> However, some systems will return a "PCI Error Response" instead. This
>> value, along with an error code of 0 from the PCI config access, will
>> confuse callers of the amd_smn_read() function.
> 
> Yes, but it hasn't so far. It is all pretty-much, a hypothetical, "what
> if" thing.
> 
> Sure, if that error would cause a serious issue on some system, by any
> means. But just because it might potentially happen... Meh.
> 
>> But I think it's fine to drop the stable tag after reading through the
>> rules again. I'll do option 2 or 3 if there's interest for specific
>> branches. And the cherry-pick thing should be easy to do if all the
>> prerequisites are already upstream.
> 
> Just wait until some real issue happens. Otherwise, you'll be pretty
> much wasting time and energy.
> 
> And, btw, people should upgrade their kernels on a regular basis - not
> run old, Frankenstein backported crap and think they've got the best of
> both worlds.
>

Okay, no problem.

Thanks,
Yazen