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Date: Sun, 26 Aug 2018 15:15:41 -0700
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: TLB flushes on fixmap changes
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To: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>, Andy Lutomirski <luto@amacapital.net>, Andy Lutomirski <luto@kernel.org>, Masami Hiramatsu <mhiramat@kernel.org>, Nadav Amit <nadav.amit@gmail.com>, Linus Torvalds <torvalds@linux-foundation.org>, Paolo Bonzini <pbonzini@redhat.com>, Jiri Kosina <jkosina@suse.cz>, Peter Zijlstra <peterz@infradead.org>, Will Deacon <will.deacon@arm.com>, Benjamin Herrenschmidt <benh@au1.ibm.com>, Nick Piggin <npiggin@gmail.com>, the arch/x86 maintainers <x86@kernel.org>, Borislav Petkov <bp@alien8.de>, Rik van Riel <riel@surriel.com>, Jann Horn <jannh@google.com>, Adin Scannell <ascannell@google.com>, Dave Hansen <dave.hansen@intel.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, David Miller <davem@davemloft.net>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Michael Ellerman <mpe@ellerman.id.au>

On Sun, Aug 26, 2018 at 03:03:59PM -0700, Kees Cook wrote:
> I thought the point was that the implementation I suggested was
> NMI-proof? (And in reading Documentation/preempt-locking.txt it sounds
> like disabling interrupts is redundant to preempt_disable()? But I
> don't understand how; it looks like the preempt stuff is advisory?)

Oter way round; disabling interrupts implicitly disables preemption