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References: <cover.1497415951.git.luto@kernel.org> <039935bc914009103fdaa6f72f14980c19562de5.1497415951.git.luto@kernel.org>
 <cc8596e6-8c6c-eb0c-4d59-ee3b97fe881f@intel.com>
From: Andy Lutomirski <luto@kernel.org>
Date: Wed, 14 Jun 2017 15:42:59 -0700
Message-ID: <CALCETrUi44LiuyizVh=bfntnvebiEVbvJz+7AwdyT647CJSZcg@mail.gmail.com>
Subject: Re: [PATCH v2 05/10] x86/mm: Rework lazy TLB mode and TLB freshness tracking
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To: Dave Hansen <dave.hansen@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Borislav Petkov <bp@alien8.de>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Nadav Amit <nadav.amit@gmail.com>, Rik van Riel <riel@redhat.com>, Arjan van de Ven <arjan@linux.intel.com>, Peter Zijlstra <peterz@infradead.org>, Andrew Banman <abanman@sgi.com>, Mike Travis <travis@sgi.com>, Dimitri Sivanich <sivanich@sgi.com>, Juergen Gross <jgross@suse.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>

On Wed, Jun 14, 2017 at 3:33 PM, Dave Hansen <dave.hansen@intel.com> wrote:
> On 06/13/2017 09:56 PM, Andy Lutomirski wrote:
>> -     if (cpumask_test_cpu(cpu, &batch->cpumask))
>> +     if (cpumask_test_cpu(cpu, &batch->cpumask)) {
>> +             local_irq_disable();
>>               flush_tlb_func_local(&info, TLB_LOCAL_SHOOTDOWN);
>> +             local_irq_enable();
>> +     }
>> +
>
> Could you talk a little about why this needs to be local_irq_disable()
> and not preempt_disable()?  Is it about the case where somebody is
> trying to call flush_tlb_func_*() from an interrupt handler?

It's to prevent flush_tlb_func_local() and flush_tlb_func_remote()
from being run concurrently, which would cause flush_tlb_func_common()
to be reentered.  Either we'd need to be very careful in
flush_tlb_func_common() to avoid races if this happened, or we could
just disable interrupts around flush_tlb_func_local().  The latter is
fast and easy.

--Andy

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