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

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Message-ID: <20181017160050.rw6tl2dzqiozbq3m@linutronix.de>
Date:   Wed, 17 Oct 2018 18:00:51 +0200
From:   'Sebastian Andrzej Siewior' <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
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 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?

> > So should we just replace it with cpa_flush_all() ?
> 
> The comment there suggests that will deadlock, supposedly because the
> kernel_map_page() call can happen with IRQs disabled or such.
> 
> I've not deeply looked at this.

free_pages() / __free_pages() for instance ends may end up in
kernel_map_pages() (via free_pages_prepare()). And if this is invoked
with disabled interrupts…

Sebastian