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From: Will Deacon <will@kernel.org>
To: Alex Belits <abelits@marvell.com>
Cc: "mark.rutland@arm.com" <mark.rutland@arm.com>,
	"mingo@kernel.org" <mingo@kernel.org>,
	"davem@davemloft.net" <davem@davemloft.net>,
	"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	Prasun Kapoor <pkapoor@marvell.com>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"frederic@kernel.org" <frederic@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [EXT] Re: [PATCH v3 03/13] task_isolation: add instruction synchronization memory barrier
Date: Mon, 20 Apr 2020 13:23:51 +0100
Message-ID: <20200420122350.GB12889@willie-the-truck> (raw)
In-Reply-To: <e4d2cda6f011e80a0d8e482b85bca1c57665fcfd.camel@marvell.com>

On Sun, Apr 19, 2020 at 05:02:01AM +0000, Alex Belits wrote:
> On Wed, 2020-04-15 at 13:44 +0100, Mark Rutland wrote:
> > On Thu, Apr 09, 2020 at 03:17:40PM +0000, Alex Belits wrote:
> > > Some architectures implement memory synchronization instructions
> > > for
> > > instruction cache. Make a separate kind of barrier that calls them.
> > 
> > Modifying the instruction caches requries more than an ISB, and the
> > 'IMB' naming implies you're trying to order against memory accesses,
> > which isn't what ISB (generally) does.
> > 
> > What exactly do you want to use this for?
> 
> I guess, there should be different explanation and naming.
> 
> The intention is to have a separate barrier that causes cache
> synchronization event, for use in architecture-independent code. I am
> not sure, what exactly it should do to be implemented in architecture-
> independent manner, so it probably only makes sense along with a
> regular memory barrier.
> 
> The particular place where I had to use is the code that has to run
> after isolated task returns to the kernel. In the model that I propose
> for task isolation, remote context synchronization is skipped while
> task is in isolated in userspace (it doesn't run kernel, and kernel
> does not modify its userspace code, so it's harmless until entering the
> kernel).

> So it will skip the results of kick_all_cpus_sync() that was
> that was called from flush_icache_range() and other similar places.
> This means that once it's out of userspace, it should only run
> some "safe" kernel entry code, and then synchronize in some manner that
> avoids race conditions with possible IPIs intended for context
> synchronization that may happen at the same time. My next patch in the
> series uses it in that one place.
> 
> Synchronization will have to be implemented without a mandatory
> interrupt because it may be triggered locally, on the same CPU. On ARM,
> ISB is definitely necessary there, however I am not sure, how this
> should look like on x86 and other architectures. On ARM this probably
> still should be combined with a real memory barrier and cache
> synchronization, however I am not entirely sure about details. Would
> it make more sense to run DMB, IC and ISB? 

IIUC, we don't need to do anything on arm64 because taking an exception acts
as a context synchronization event, so I don't think you should try to
expose this as a new barrier macro. Instead, just make it a pre-requisite
that architectures need to ensure this behaviour when entering the kernel
from userspace if they are to select HAVE_ARCH_TASK_ISOLATION.

That way, it's /very/ similar to what we do for MEMBARRIER_SYNC_CORE, the
only real different being that that is concerned with return-to-user rather
than entry-from-user.

See Documentation/features/sched/membarrier-sync-core/arch-support.txt

Will

  reply index

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-04 16:01 [PATCH 00/12] "Task_isolation" mode Alex Belits
2020-03-04 16:03 ` [PATCH 01/12] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits
2020-03-04 16:04 ` [PATCH 02/12] task_isolation: vmstat: add vmstat_idle function Alex Belits
2020-03-04 16:07 ` [PATCH 03/12] task_isolation: userspace hard isolation from kernel Alex Belits
2020-03-05 18:33   ` Frederic Weisbecker
2020-03-08  5:32     ` [EXT] " Alex Belits
2020-04-28 14:12     ` Marcelo Tosatti
2020-03-06 15:26   ` Frederic Weisbecker
2020-03-08  6:06     ` [EXT] " Alex Belits
2020-03-06 16:00   ` Frederic Weisbecker
2020-03-08  7:16     ` [EXT] " Alex Belits
2020-03-04 16:08 ` [PATCH 04/12] task_isolation: Add task isolation hooks to arch-independent code Alex Belits
2020-03-04 16:09 ` [PATCH 05/12] task_isolation: arch/x86: enable task isolation functionality Alex Belits
2020-03-04 16:10 ` [PATCH 06/12] task_isolation: arch/arm64: " Alex Belits
2020-03-04 16:31   ` Mark Rutland
2020-03-08  4:48     ` [EXT] " Alex Belits
2020-03-04 16:11 ` [PATCH 07/12] task_isolation: arch/arm: " Alex Belits
2020-03-04 16:12 ` [PATCH 08/12] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-03-06 16:03   ` Frederic Weisbecker
2020-03-08  7:28     ` [EXT] " Alex Belits
2020-03-09  2:38       ` Frederic Weisbecker
2020-03-04 16:13 ` [PATCH 09/12] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits
2020-03-04 16:14 ` [PATCH 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits
2020-03-04 16:15 ` [PATCH 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-03-06 15:34   ` Frederic Weisbecker
2020-03-08  6:48     ` [EXT] " Alex Belits
2020-03-09  2:28       ` Frederic Weisbecker
2020-03-04 16:16 ` [PATCH 12/12] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits
2020-03-08  3:42 ` [PATCH v2 00/12] "Task_isolation" mode Alex Belits
2020-03-08  3:44   ` [PATCH v2 01/12] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits
2020-03-08  3:46   ` [PATCH v2 02/12] task_isolation: vmstat: add vmstat_idle function Alex Belits
2020-03-08  3:47   ` [PATCH v2 03/12] task_isolation: userspace hard isolation from kernel Alex Belits
     [not found]     ` <20200307214254.7a8f6c22@hermes.lan>
2020-03-08  7:33       ` [EXT] " Alex Belits
2020-03-27  8:42     ` Marta Rybczynska
2020-04-06  4:31     ` Kevyn-Alexandre Paré
2020-04-06  4:43     ` Kevyn-Alexandre Paré
2020-03-08  3:48   ` [PATCH v2 04/12] task_isolation: Add task isolation hooks to arch-independent code Alex Belits
2020-03-08  3:49   ` [PATCH v2 05/12] task_isolation: arch/x86: enable task isolation functionality Alex Belits
2020-03-08  3:50   ` [PATCH v2 06/12] task_isolation: arch/arm64: " Alex Belits
2020-03-09 16:59     ` Mark Rutland
2020-03-08  3:52   ` [PATCH v2 07/12] task_isolation: arch/arm: " Alex Belits
2020-03-08  3:53   ` [PATCH v2 08/12] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-03-08  3:54   ` [PATCH v2 09/12] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits
2020-03-08  3:55   ` [PATCH v2 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits
2020-04-06  4:27     ` Kevyn-Alexandre Paré
2020-03-08  3:56   ` [PATCH v2 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-03-08  3:57   ` [PATCH v2 12/12] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits
2020-04-09 15:09   ` [PATCH v3 00/13] "Task_isolation" mode Alex Belits
2020-04-09 15:15     ` [PATCH 01/13] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits
2020-04-09 15:16     ` [PATCH 02/13] task_isolation: vmstat: add vmstat_idle function Alex Belits
2020-04-09 15:17     ` [PATCH v3 03/13] task_isolation: add instruction synchronization memory barrier Alex Belits
2020-04-15 12:44       ` Mark Rutland
2020-04-19  5:02         ` [EXT] " Alex Belits
2020-04-20 12:23           ` Will Deacon [this message]
2020-04-20 12:36             ` Mark Rutland
2020-04-20 13:55               ` Will Deacon
2020-04-21  7:41                 ` Will Deacon
2020-04-20 12:45           ` Mark Rutland
2020-04-09 15:20     ` [PATCH v3 04/13] task_isolation: userspace hard isolation from kernel Alex Belits
2020-04-09 18:00       ` Andy Lutomirski
2020-04-19  5:07         ` Alex Belits
2020-04-09 15:21     ` [PATCH 05/13] task_isolation: Add task isolation hooks to arch-independent code Alex Belits
2020-04-09 15:22     ` [PATCH 06/13] task_isolation: arch/x86: enable task isolation functionality Alex Belits
2020-04-09 15:23     ` [PATCH v3 07/13] task_isolation: arch/arm64: " Alex Belits
2020-04-22 12:08       ` Catalin Marinas
2020-04-09 15:24     ` [PATCH v3 08/13] task_isolation: arch/arm: " Alex Belits
2020-04-09 15:25     ` [PATCH v3 09/13] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-04-09 15:26     ` [PATCH v3 10/13] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits
2020-04-09 15:27     ` [PATCH v3 11/13] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits
2020-04-09 15:27     ` [PATCH v3 12/13] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-04-09 15:28     ` [PATCH v3 13/13] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits

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