Messages in this thread | | | Date | Tue, 18 May 2021 13:35:27 -0700 | From | Pawan Gupta <> | Subject | Re: [v6 1/1] x86/bugs: Implement mitigation for Predictive Store Forwarding |
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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
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