linux-kernel - Re: [PATCH] x86/mm/pat: Fix missing preemption disable for __native_flush

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Message-ID: <CAPcyv4hXzBT1LkEdBYw_mkrKV+SK1LRE2PwJ5=T+e7GxWbXaNQ@mail.gmail.com>
Date:   Sat, 10 Nov 2018 15:57:42 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        stable <stable@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/mm/pat: Fix missing preemption disable for __native_flush_tlb()

On Fri, Nov 9, 2018 at 4:22 PM Andy Lutomirski <luto@...capital.net> wrote:
>
>
>
> > On Nov 9, 2018, at 4:05 PM, Dan Williams <dan.j.williams@...el.com> 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 don’t think I agree with the patch. If you call __flush_tlb_all() in a context where you might be *migrated*, then there’s a bug. We could change the code to allow this particular use by checking that we haven’t done SMP init yet, perhaps.

Hmm, are saying the entire kernel_physical_mapping_init() sequence
needs to run with pre-emption disabled?