Re: [PATCH RESEND v3] x86/split_lock: fix delayed detection enabling

[Maksim Davydov]

Hi!
Thanks a lot!
I've rebased onto the newest master
https://lore.kernel.org/lkml/20241125221147.932377-1-davydov-max@xxxxxxxxxxxxxx/

On 11/20/24 22:16, Guilherme G. Piccoli wrote:
> On 13/11/2024 11:23, Maksim Davydov wrote:
> > If the warn mode with disabled mitigation mode is used, then on each
> > CPU where the split lock occurred detection will be disabled in order to
> > make progress and delayed work will be scheduled, which then will enable
> > detection back. Now it turns out that all CPUs use one global delayed
> > work structure. This leads to the fact that if a split lock occurs on
> > several CPUs at the same time (within 2 jiffies), only one CPU will
> > schedule delayed work, but the rest will not. The return value of
> > schedule_delayed_work_on() would have shown this, but it is not checked
> > in the code.
> >
> > A diagram that can help to understand the bug reproduction:
> > https://lore.kernel.org/all/2cd54041-253b-4e78-b8ea-dbe9b884ff9b@xxxxxxxxxxxxxx/
> >
> > In order to fix the warn mode with disabled mitigation mode, delayed work
> > has to be a per-CPU.
> >
> > v3 -> v2:
> > * place and time of the per-CPU structure initialization were changed.
> >    initcall doesn't seem to be a good place for it, so deferred
> >    initialization is used.
> >
> > Fixes: 727209376f49 ("x86/split_lock: Add sysctl to control the misery mode")
> > Signed-off-by: Maksim Davydov <davydov-max@xxxxxxxxxxxxxx>
> > ---
> >   arch/x86/kernel/cpu/intel.c | 20 ++++++++++++++++----
> >   1 file changed, 16 insertions(+), 4 deletions(-)
>
>
> Hi Maksim, thanks for resubmitting again. I think that is indeed a valid
> fix, but what I've also noticed is that recently (as in this week) the
> code changed from the intel.c file to a more generic one, since AMD is
> enabling split lock detection in their CPUs apparently [0].
>
> So, I'd suggest you to rebase against 6.13-rc, that would likely
> increase the chances of a merge. Once you do that, I can try to test it
> as well, though I don't personally have an Intel CPU with that feature
> (but some friends have it).
>
> Cheers,
>
>
> Guilherme
>
>
> [0] https://lore.kernel.org/r/ZzuBNj4JImJGUNJc@xxxxxxxxx/

--
Best regards,
Maksim Davydov