linux-kernel - Re: [PATCH v2] x86,acpi: Limit "Dummy wait" workaround to older AMD and Intel processors

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Date:   Fri, 23 Sep 2022 21:55:02 +0530
From:   K Prateek Nayak <kprateek.nayak@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, rafael@...nel.org, lenb@...nel.org,
        linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
        dave.hansen@...ux.intel.com, tglx@...utronix.de, andi@...as.de,
        puwen@...on.cn, mario.limonciello@....com, peterz@...radead.org,
        rui.zhang@...el.com, gpiccoli@...lia.com,
        daniel.lezcano@...aro.org, ananth.narayan@....com,
        gautham.shenoy@....com, Calvin Ong <calvin.ong@....com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] x86,acpi: Limit "Dummy wait" workaround to older AMD
 and Intel processors

Hello Boris,

On 9/23/2022 9:16 PM, Borislav Petkov wrote:
> On Fri, Sep 23, 2022 at 09:08:01PM +0530, K Prateek Nayak wrote:
>> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
>> index ef4775c6db01..fcd3617ed315 100644
>> --- a/arch/x86/include/asm/cpufeatures.h
>> +++ b/arch/x86/include/asm/cpufeatures.h
>> @@ -460,5 +460,6 @@
>>  #define X86_BUG_MMIO_UNKNOWN		X86_BUG(26) /* CPU is too old and its MMIO Stale Data status is unknown */
>>  #define X86_BUG_RETBLEED		X86_BUG(27) /* CPU is affected by RETBleed */
>>  #define X86_BUG_EIBRS_PBRSB		X86_BUG(28) /* EIBRS is vulnerable to Post Barrier RSB Predictions */
>> +#define X86_BUG_STPCLK			X86_BUG(29) /* STPCLK# signal does not get asserted in time during IOPORT based C-state entry */
> 
> What for?
> 
> Did you not see this thread?
> 
> https://lore.kernel.org/r/78d13a19-2806-c8af-573e-7f2625edfab8@intel.com
> 

Yes, I did see the patch, but Andreas replied to Dave's patch attached
in v1 saying that he had seen this issue with AMD Athlon on a VIA
chipset back in 2006. (https://lore.kernel.org/lkml/Yyy6l94G0O2B7Yh1@rhlx01.hs-esslingen.de/)
Therefore, Dave's patch is not sufficient.

Dave suggested the use of AMD vendor and family check, but Peter then
pointed out that we would also need the Hygon vendor check.

Hence I worked on the v2 which addressed these with the help of
X86_BUG_STPCLK so that we can avoid vendor specific checks inside the
common acpi code.
--
Thanks and Regards,
Prateek