lkml.org 
[lkml]   [2021]   [May]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [v6 1/1] x86/bugs: Implement mitigation for Predictive Store Forwarding
On 18.05.2021 07:27, Saripalli, RK wrote:
>
>
>On 5/17/2021 9:55 PM, Randy Dunlap wrote:
>> Hi again,
>>
>> On 5/17/21 3:00 PM, Ramakrishna Saripalli wrote:
>>> From: Ramakrishna Saripalli <rk.saripalli@amd.com>
>>>
>>> Certain AMD processors feature a new technology called Predictive Store
>>> Forwarding (PSF).
>>>
>>> PSF is a micro-architectural optimization designed to improve the
>>> performance of code execution by predicting dependencies between
>>> loads and stores.
>>>
>>> Incorrect PSF predictions can occur due to two reasons.
>>>
>> ...
>>
>>>
>>> Kernel parameter predictive_store_fwd_disable has the following values
>>>
>>> - on. Disable PSF on all CPUs.
>>>
>>> - off. Enable PSF on all CPUs.
>>> This is also the default setting.
>>>
>>> Signed-off-by: Ramakrishna Saripalli<rk.saripalli@amd.com>
>>> ---
>>> .../admin-guide/kernel-parameters.txt | 5 +
>>> arch/x86/include/asm/cpufeatures.h | 1 +
>>> arch/x86/include/asm/msr-index.h | 2 +
>>> arch/x86/include/asm/nospec-branch.h | 6 ++
>>> arch/x86/kernel/cpu/bugs.c | 94 +++++++++++++++++++
>>> 5 files changed, 108 insertions(+)
>>>
>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>> index 04545725f187..a5f694dccb24 100644
>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>> @@ -3940,6 +3940,11 @@
>>> Format: {"off"}
>>> Disable Hardware Transactional Memory
>>>
>>> + predictive_store_fwd_disable= [X86] This option controls PSF.
>>> + off - Turns on PSF.
>>> + on - Turns off PSF.
>>> + default : off.
>>
>>
>> and as I did earlier, I still object to "off" meaning PSF is on
>> and "on" meaning that PSF is off.
>>
>> It's not at all user friendly.
>>
>> If it's done this way because that's how the h/w bit is defined/used,
>> that's not a good excuse IMHO.
>>
>> Hm, it sorta seems to be a common "theme" when dealing with mitigations.
>> And too late to fix that.
>
>Based on previous feedback from Thomas Gleixner, I reworded this as a mitigation instead of as a "feature".
>In that vein, all the mitigation code moved into bugs.c like other mitigations, similar to
>spec_control_bypass_disable with an ON/OFF but no prctl/seccomp/auto.

Maybe change the help text to something like:

on - Turns on PSF mitigation.
off - Turns off PSF mitigation.

Thanks,
Pawan

\
 
 \ /
  Last update: 2021-05-18 22:36    [W:0.173 / U:0.164 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site