linux-kernel - Re: [PATCH 1/4] mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race

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Date:   Fri, 28 Aug 2020 13:15:25 +0200
From:   peterz@...radead.org
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 1/4] mm: fix exec activate_mm vs TLB shootdown and lazy
 tlb switching race

On Fri, Aug 28, 2020 at 08:00:19PM +1000, Nicholas Piggin wrote:

> Closing this race only requires interrupts to be disabled while ->mm
> and ->active_mm are being switched, but the TLB problem requires also
> holding interrupts off over activate_mm. Unfortunately not all archs
> can do that yet, e.g., arm defers the switch if irqs are disabled and
> expects finish_arch_post_lock_switch() to be called to complete the
> flush; um takes a blocking lock in activate_mm().

ARM at least has activate_mm() := switch_mm(), so it could be made to
work.