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From: Will Deacon <will@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"peterz@infradead.org" <peterz@infradead.org>,
	Alex Belits <abelits@marvell.com>,
	"frederic@kernel.org" <frederic@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"davem@davemloft.net" <davem@davemloft.net>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
	Prasun Kapoor <pkapoor@marvell.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@kernel.org" <mingo@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: Tue, 21 Apr 2020 08:41:02 +0100	[thread overview]
Message-ID: <20200421074101.GA15021@willie-the-truck> (raw)
In-Reply-To: <20200420135523.GA18711@willie-the-truck>

On Mon, Apr 20, 2020 at 02:55:23PM +0100, Will Deacon wrote:
> On Mon, Apr 20, 2020 at 01:36:28PM +0100, Mark Rutland wrote:
> > On Mon, Apr 20, 2020 at 01:23:51PM +0100, Will Deacon wrote:
> > > 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.
> > 
> > The CSE from the exception isn't sufficient here, because it needs to
> > occur after the CPU has re-registered to receive IPIs for
> > kick_all_cpus_sync(). Otherwise there's a window between taking the
> > exception and re-registering where a necessary context synchronization
> > event can be missed. e.g.
> > 
> > CPU A				CPU B
> > [ Modifies some code ]		
> > 				[ enters exception ]
> > [ D cache maintenance ]
> > [ I cache maintenance ]
> > [ IPI ]				// IPI not taken
> >   ...				[ register for IPI ] 
> > [ IPI completes ] 
> > 				[ execute stale code here ]
> 
> Thanks.
> 
> > However, I think 'IMB' is far too generic, and we should have an arch
> > hook specific to task isolation, as it's far less likely to be abused as
> > IMB will.
> 
> What guarantees we don't run any unsynchronised module code between
> exception entry and registering for the IPI? It seems like we'd want that
> code to run as early as possible, e.g. as part of
> task_isolation_user_exit() but that doesn't seem to be what's happening.

Sorry, I guess that's more a question for Alex.

Alex -- do you think we could move the "register for IPI" step earlier
so that it's easier to reason about the code that runs in the dead zone
during exception entry?

Will

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  reply	other threads:[~2020-04-21  7:41 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <4473787e1b6bc3cc226067e8d122092a678b63de.camel@marvell.com>
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
2020-04-20 12:36             ` Mark Rutland
2020-04-20 13:55               ` Will Deacon
2020-04-21  7:41                 ` Will Deacon [this message]
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
     [not found] ` <ef365b5754ffc07980ed1df6ac8531a8ff590a17.camel@marvell.com>
     [not found]   ` <20200304163103.GJ3575@lakrids.cambridge.arm.com>
2020-03-08  4:48     ` [EXT] Re: [PATCH 06/12] task_isolation: arch/arm64: enable task isolation functionality Alex Belits
     [not found] ` <36d84b8dd168a38e6a56549dedc15dd6ebf8c09e.camel@marvell.com>
     [not found]   ` <20200305183313.GA29033@lenoir>
2020-03-08  5:32     ` [EXT] Re: [PATCH 03/12] task_isolation: userspace hard isolation from kernel Alex Belits
     [not found]   ` <20200306152632.GB8590@lenoir>
2020-03-08  6:06     ` Alex Belits
     [not found] ` <dfa5e0e9f34e6ff0ef048c81bc70496354f31300.camel@marvell.com>
     [not found]   ` <20200306153446.GC8590@lenoir>
2020-03-08  6:48     ` [EXT] Re: [PATCH 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-03-09  2:28       ` Frederic Weisbecker
     [not found] ` <d7ce01e57d4a35b126e1cb96a63109eaa9781cb6.camel@marvell.com>
     [not found]   ` <20200306160341.GE8590@lenoir>
2020-03-08  7:28     ` [EXT] Re: [PATCH 08/12] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-03-09  2:38       ` Frederic Weisbecker

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