lkml.org 
[lkml]   [2020]   [Jan]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v12] x86/split_lock: Enable split lock detection by kernel
On Wed, Jan 22, 2020 at 11:24:34PM +0000, Luck, Tony wrote:
> >> +static enum split_lock_detect_state sld_state = sld_warn;
> >> +
> >
> > This sets sld_state to sld_warn even on CPUs that don't support
> > split-lock detection. split_lock_init will then try to read/write the
> > MSR to turn it on. Would it be better to initialize it to sld_off and
> > set it to sld_warn in split_lock_setup instead, which is only called if
> > the CPU supports the feature?
>
> I've lost some bits of this patch series somewhere along the way :-( There
> was once code to decide whether the feature was supported (either with
> x86_match_cpu() for a couple of models, or using the architectural test
> based on some MSR bits. I need to dig that out and put it back in. Then
> stuff can check X86_FEATURE_SPLIT_LOCK before wandering into code
> that messes with MSRs

That code is still there (cpu_set_core_cap_bits). The issue is that with
the initialization here, nothing ever sets sld_state to sld_off if the
feature isn't supported.

v10 had a corresponding split_lock_detect_enabled that was
0-initialized, but Peter's patch as he sent out had the flag initialized
to sld_warn.

>
> >> + if (!split_lock_detect_enabled())
> >> + return;
> >
> > This misses one comment from Sean [1] that this check should be dropped,
> > otherwise user-space alignment check via EFLAGS.AC will get ignored when
> > split lock detection is disabled.
>
> Ah yes. Good catch. Will fix.
>
> Thanks for the review.
>
> -Tony

\
 
 \ /
  Last update: 2020-01-23 01:46    [W:0.374 / U:0.328 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site