Re: x86/mm: Finishing off the fix for a should_flush_tlb race

[Seth Forshee <sforshee@kernel.org>]

On Tue, Feb 17, 2026 at 09:12:43AM -0600, Seth Forshee wrote:
> On Fri, Oct 10, 2025 at 01:45:45PM -0700, Dave Hansen wrote:
> > On 10/9/25 07:01, Stephen Dolan wrote:
> > > That way, either shootdown sees LOADED_MM_SWITCHING and sends an IPI, or
> > > switch_mm_irqs_off sees the updated tlb_gen. The problem in both cases
> > > is about the *before*-ness in switch_mm_irqs_off:
> > > 
> > >   - in the latest tree, there isn't enough fencing to enforce this
> > >     ordering.
> > 
> > Stephen, thank you again for the stunningly great bug report!
> > 
> > I'll plan to stick the upstream fix into our x86/urgent pile early next
> > week.
> > 
> > >   - in the stable kernel trees (6.1, 6.6, 6.12), the code is in the
> > >     wrong order.
> > 
> > This fix also makes sense to me. It's a bummer that the stable fixes are
> > diverging, but I don't have a better idea. So:
> > 
> > Acked-by: Dave Hansen <dave.hansen@intel.com>
> > 
> > It would be best if you could just submit that patch directly to the
> > stable trees:
> > 
> > https://www.kernel.org/doc/Documentation/process/stable-kernel-rules.rst
> > 
> > after the equivalent upstream fix lands (even though it is a different
> > logical patch).
> 
> I wanted to check on the status of the stable patches, since I see the
> upstream fix went into 6.18 but there's still no fix in the 6.12 stable
> tree. We've been seeing segfaults during a test case with 6.12, and
> after bisecting we found that reverting both "x86/mm: Eliminate window
> where TLB flushes may be inadvertently skipped" and "x86/mm/tlb: Only
> trim the mm_cpumask once a second" seems to get rid of the segfaults.
> I'll try to get some testing with the proposed stable patch today.

Sorry, had something wrong in my mail config that messed up the From:
address in the last email. Please reply to this addrees instead.