Re: [PATCH RT] x86/mm/pat: disable preemption __split_large_page() after spin_lock()

[Scott Wood]

On Thu, 2018-12-13 at 17:44 +0100, Sebastian Andrzej Siewior wrote:
> Commit "x86/mm/pat: Disable preemption around __flush_tlb_all()" added a
> warning if __flush_tlb_all() is invoked in preemptible context. On !RT
> the warning does not trigger because a spin lock is acquired which
> disables preemption. On RT the spin lock does not disable preemption and
> so the warning is seen.
> 
> Disable preemption to avoid the warning in __flush_tlb_all().
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

FWIW, that __flush_tlb_all() can probably just be removed.  It was added as
a partial workaround for an erratum, but since it didn't completely solve
the problem, hugepages were disabled on the affected chips in commit
7a0fc404ae66377 ("x86: Disable large pages on CPUs with Atom erratum
AAE44").  I was going to send a (non-RT) patch removing the flush but in
4.20 commit c0a759abf5a68 ("x86/mm/cpa: Move flush_tlb_all()") reworked the
code to make it moot.

-Scott