Re: [PATCH] x86/mm/pat: Fix missing preemption disable for __native_flush_tlb()

[Dan Williams]

[ added Kirill ]

On Sat, Nov 10, 2018 at 4:19 PM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> > On Nov 10, 2018, at 3:57 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> >
> >> On Fri, Nov 9, 2018 at 4:22 PM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> >>
> >>
> >>
> >>> On Nov 9, 2018, at 4:05 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> >>>
> >>> Commit f77084d96355 "x86/mm/pat: Disable preemption around
> >>> __flush_tlb_all()" addressed a case where __flush_tlb_all() is called
> >>> without preemption being disabled. It also left a warning to catch other
> >>> cases where preemption is not disabled. That warning triggers for the
> >>> memory hotplug path which is also used for persistent memory enabling:
> >>
> >> I donât think I agree with the patch. If you call __flush_tlb_all() in a context where you might be *migrated*, then thereâs a bug. We could change the code to allow this particular use by checking that we havenât done SMP init yet, perhaps.
> >
> > Hmm, are saying the entire kernel_physical_mapping_init() sequence
> > needs to run with pre-emption disabled?
>
> If it indeed can run late in boot or after boot, then it sure looks buggy. Either the __flush_tlb_all() should be removed or it should be replaced with flush_tlb_kernel_range(). Itâs unclear to me why a flush is needed at all, but if itâs needed, surely all CPUs need flushing.

Yeah, I don't think __flush_tlb_all() is needed at
kernel_physical_mapping_init() time, and at
kernel_physical_mapping_remove() time we do a full flush_tlb_all().

Kirill?