From: Catalin Marinas <catalin.marinas@arm.com>
To: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: linux-arch@vger.kernel.org, Szabolcs Nagy <szabolcs.nagy@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Peter Collingbourne <pcc@google.com>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Will Deacon <will@kernel.org>,
Dave P Martin <Dave.Martin@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v7 18/29] arm64: mte: Allow user control of the tag check mode via prctl()
Date: Wed, 22 Jul 2020 12:09:51 +0100 [thread overview]
Message-ID: <20200722110950.GB27540@gaia> (raw)
In-Reply-To: <e9feb87e-41a8-17e6-eeba-4038da3bdde2@arm.com>
On Mon, Jul 20, 2020 at 04:30:35PM +0100, Kevin Brodsky wrote:
> On 15/07/2020 18:08, Catalin Marinas wrote:
> > +void mte_thread_switch(struct task_struct *next)
> > +{
> > + if (!system_supports_mte())
> > + return;
> > +
> > + /* avoid expensive SCTLR_EL1 accesses if no change */
> > + if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0)
>
> I think this could be improved by checking whether `next` is a kernel
> thread, in which case thread.sctlr_tcf0 is 0 but there is no point in
> setting SCTLR_EL1.TCF0, since there should not be any access via TTBR0.
It's not about kernel or user thread here. kthread_use_mm() (just
use_mm() in older kernels) would set an mm on a kernel thread,
temporarily making it behave as a user one. Since the sctlr_tcf0 is per
thread, not per mm, we need to switch to the default TCF0 for kthreads
so that user accesses (if use_mm() is called) don't generate any tag
check faults. Note that switch_mm() does not touch TCF0.
If we did allow a global, per-mm TCF0 setting, such kthreads could only
handle synchronous faults and no SIGSEGV generated (as we do with
copy_{from,to}_user() for normal threads).
If we want to revisit per-thread vs per-mm TCF0 setting, now is the
time.
--
Catalin
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next prev parent reply other threads:[~2020-07-22 11:11 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200715170844.30064-1-catalin.marinas@arm.com>
[not found] ` <20200715170844.30064-30-catalin.marinas@arm.com>
2020-07-27 16:36 ` [PATCH v7 29/29] arm64: mte: Add Memory Tagging Extension documentation Szabolcs Nagy
2020-07-28 11:08 ` Dave Martin
2020-07-28 14:53 ` Szabolcs Nagy
2020-07-28 19:59 ` Catalin Marinas
2020-08-03 12:43 ` Szabolcs Nagy
2020-08-07 15:19 ` Catalin Marinas
2020-08-10 14:13 ` Szabolcs Nagy
2020-08-11 17:20 ` Catalin Marinas
2020-08-12 12:45 ` Szabolcs Nagy
2020-08-19 9:54 ` Catalin Marinas
2020-08-20 16:43 ` Szabolcs Nagy
2020-08-20 17:27 ` Paul Eggert
2020-08-22 11:31 ` Catalin Marinas
2020-08-22 11:28 ` Catalin Marinas
[not found] ` <20200715170844.30064-19-catalin.marinas@arm.com>
2020-07-20 15:30 ` [PATCH v7 18/29] arm64: mte: Allow user control of the tag check mode via prctl() Kevin Brodsky
2020-07-20 17:00 ` Dave Martin
2020-07-22 10:28 ` Catalin Marinas
2020-07-23 19:33 ` Kevin Brodsky
2020-07-22 11:09 ` Catalin Marinas [this message]
2020-08-04 19:34 ` Kevin Brodsky
2020-08-05 9:24 ` Catalin Marinas
[not found] ` <20200715170844.30064-23-catalin.marinas@arm.com>
2020-08-13 14:01 ` [PATCH v7 22/29] arm64: mte: ptrace: Add PTRACE_{PEEK,POKE}MTETAGS support Luis Machado
2020-08-22 10:56 ` Catalin Marinas
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