Re: [PATCH 1/3] x86/mm/pat: Disable preemption around __flush_tlb_all()

From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Laight <David.Laight@ACULAB.COM>,
	'Sebastian Andrzej Siewior' <bigeasy@linutronix.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 1/3] x86/mm/pat: Disable preemption around __flush_tlb_all()
Date: Wed, 17 Oct 2018 13:17:18 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1810171315250.6000@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20181017111145.GJ3121@hirez.programming.kicks-ass.net>

On Wed, 17 Oct 2018, Peter Zijlstra wrote:
> On Wed, Oct 17, 2018 at 09:54:38AM +0000, David Laight wrote:
> > >  	 * We should perform an IPI and flush all tlbs,
> > >  	 * but that can deadlock->flush only current cpu:
> > >  	 */
> > > +	preempt_disable();
> > >  	__flush_tlb_all();
> > > +	preempt_enable();
> > 
> > Can it make any sense to flush the tlb with preemption enabled?
> > Surely preemption must be disabled over something else as well?
> 
> This code is fishy anyway, for only doing that local invalidate.
> 
> 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.

So should we just replace it with cpa_flush_all() ?

Thanks,

	tglx