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From: Andy Lutomirski <luto@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Nicholas Piggin <npiggin@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>, Anton Blanchard <anton@ozlabs.org>,
	stable <stable@vger.kernel.org>
Subject: Re: [PATCH v3 3/4] membarrier: Explicitly sync remote cores when SYNC_CORE is requested
Date: Tue, 8 Dec 2020 20:13:40 -0800	[thread overview]
Message-ID: <CALCETrW1Bw_4KwWNOV5xFFWH056BD-cb+ok7vHTeqW7ZswxopQ@mail.gmail.com> (raw)
In-Reply-To: <776b448d5f7bd6b12690707f5ed67bcda7f1d427.1607058304.git.luto@kernel.org>

On Thu, Dec 3, 2020 at 9:07 PM Andy Lutomirski <luto@kernel.org> wrote:
>
> membarrier() does not explicitly sync_core() remote CPUs; instead, it
> relies on the assumption that an IPI will result in a core sync.  On
> x86, I think this may be true in practice, but it's not architecturally
> reliable.  In particular, the SDM and APM do not appear to guarantee
> that interrupt delivery is serializing.  While IRET does serialize, IPI
> return can schedule, thereby switching to another task in the same mm
> that was sleeping in a syscall.  The new task could then SYSRET back to
> usermode without ever executing IRET.
>
> Make this more robust by explicitly calling sync_core_before_usermode()
> on remote cores.  (This also helps people who search the kernel tree for
> instances of sync_core() and sync_core_before_usermode() -- one might be
> surprised that the core membarrier code doesn't currently show up in a
> such a search.)
>

Fixes: 70216e18e519 ("membarrier: Provide core serializing command,
*_SYNC_CORE")

> Cc: stable@vger.kernel.org
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

  reply	other threads:[~2020-12-09  4:14 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-04  5:07 [PATCH v3 0/4] membarrier fixes Andy Lutomirski
2020-12-04  5:07 ` [PATCH v3 1/4] x86/membarrier: Get rid of a dubious optimization Andy Lutomirski
2020-12-09  4:10   ` Andy Lutomirski
2020-12-09  8:42   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski
2020-12-04  5:07 ` [PATCH v3 2/4] membarrier: Add an actual barrier before rseq_preempt() Andy Lutomirski
2020-12-09  4:12   ` Andy Lutomirski
2020-12-09  8:42   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski
2020-12-14 18:05     ` Andy Lutomirski
2020-12-04  5:07 ` [PATCH v3 3/4] membarrier: Explicitly sync remote cores when SYNC_CORE is requested Andy Lutomirski
2020-12-09  4:13   ` Andy Lutomirski [this message]
2020-12-09  8:42   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski
2020-12-04  5:07 ` [PATCH v3 4/4] membarrier: Execute SYNC_CORE on the calling thread Andy Lutomirski
2020-12-04 19:35   ` Mathieu Desnoyers
2020-12-09  4:15   ` Andy Lutomirski
2020-12-09  8:42   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski

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