linux-kernel - Re: [PATCH 1/3] x86/mm/pat: Disable preemption around __flush_tlb

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Message-ID: <20181017162253.GO3121@hirez.programming.kicks-ass.net>
Date:   Wed, 17 Oct 2018 18:22:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     'Sebastian Andrzej Siewior' <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        David Laight <David.Laight@...LAB.COM>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 1/3] x86/mm/pat: Disable preemption around
 __flush_tlb_all()

On Wed, Oct 17, 2018 at 06:00:51PM +0200, 'Sebastian Andrzej Siewior' wrote:
> On 2018-10-17 17:47:07 [+0200], Peter Zijlstra wrote:
> > > > Ideally we'd never ever merge anything that only does local invalidates,
> > > > on a global address space, that's just broken.
> > > 
> > > A little bit late to lament about that.
> > 
> > For this, yes :/ But for future stuff we should really not allow such
> > things anymore.
> 
> so we stay as is?

Well, we can do that preempt kludge you propose to shut up the warning I
suppose.

But a kludge it is. That code really wants a global invalidate, but we
cannot (not without massive surgery in any case).