From: Patrick Daly <pdaly@codeaurora.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>,
linux-arch@vger.kernel.org,
Vladimir Murzin <vladimir.murzin@arm.com>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
linux-mm@kvack.org, Vincenzo Frascino <vincenzo.frascino@arm.com>,
Peter Collingbourne <pcc@google.com>,
Dave P Martin <Dave.Martin@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 24/26] arm64: mte: Introduce early param to disable MTE support
Date: Thu, 21 May 2020 22:57:10 -0700 [thread overview]
Message-ID: <20200522055710.GA25791@pdaly-linux.qualcomm.com> (raw)
In-Reply-To: <20200518172054.GL9862@gaia>
On Mon, May 18, 2020 at 06:20:55PM +0100, Catalin Marinas wrote:
> On Mon, May 18, 2020 at 12:31:03PM +0100, Will Deacon wrote:
> > On Mon, May 18, 2020 at 12:26:30PM +0100, Vladimir Murzin wrote:
> > > On 5/15/20 6:16 PM, Catalin Marinas wrote:
> > > > For performance analysis it may be desirable to disable MTE altogether
> > > > via an early param. Introduce arm64.mte_disable and, if true, filter out
> > > > the sanitised ID_AA64PFR1_EL1.MTE field to avoid exposing the HWCAP to
> > > > user.
> > > >
> > > > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > > > Cc: Will Deacon <will@kernel.org>
> > > > ---
> > > >
> > > > Notes:
> > > > New in v4.
> > > >
> > > > Documentation/admin-guide/kernel-parameters.txt | 4 ++++
> > > > arch/arm64/kernel/cpufeature.c | 11 +++++++++++
> > > > 2 files changed, 15 insertions(+)
> > > >
> > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > > > index f2a93c8679e8..7436e7462b85 100644
> > > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > > @@ -373,6 +373,10 @@
> > > > arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
> > > > Format: <io>,<irq>,<nodeID>
> > > >
> > > > + arm64.mte_disable=
> > > > + [ARM64] Disable Linux support for the Memory
> > > > + Tagging Extension (both user and in-kernel).
> > > > +
> > >
> > > Should it really to take parameter (on/off/true/false)? It may lead to expectation
> > > that arm64.mte_disable=false should enable MT and, yes, double negatives make it
> > > look ugly, so if we do need parameter, can it be arm64.mte=on/off/true/false?
> >
> > I don't think "performance analysis" is a good justification for this
> > parameter tbh. We don't tend to add these options for other architectural
> > features, and I don't see why MTE is any different in this regard.
>
> There is an expectation of performance impact with MTE enabled,
> especially if it's running in synchronous mode. For the in-kernel MTE,
> we could add a parameter which sets sync vs async at boot time rather
> than a big disable knob. It won't affect user space however.
>
> The other 'justification' is if your hardware has weird unexpected
> behaviour but I'd like this handled via errata workarounds.
>
> I'll let the people who asked for this to chip in ;). I agree with you
> that we rarely add these (and I rejected a similar option a few weeks
> ago on the AMU patchset).
We've been looking into other ways this on/off behavior could be achieved.
The "arm,armv8.5-memtag" DT flag already provides what we want - meaning
that this flag could be removed if the system did not support MTE.
I did see your remark on "arm64: mte: Check the DT memory nodes for MTE support"
questioning whether it was the right approach - is this still the case?
--Patrick
--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
next prev parent reply other threads:[~2020-05-22 5:57 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-15 17:15 [PATCH v4 00/26] arm64: Memory Tagging Extension user-space support Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 01/26] arm64: mte: system register definitions Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 02/26] arm64: mte: CPU feature detection and initial sysreg configuration Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 03/26] arm64: mte: Use Normal Tagged attributes for the linear map Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 04/26] arm64: mte: Add specific SIGSEGV codes Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 05/26] arm64: mte: Handle synchronous and asynchronous tag check faults Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 06/26] mm: Add PG_ARCH_2 page flag Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 07/26] arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 08/26] arm64: mte: Tags-aware copy_page() implementation Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 09/26] arm64: mte: Tags-aware aware memcmp_pages() implementation Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 10/26] mm: Introduce arch_calc_vm_flag_bits() Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 11/26] arm64: mte: Add PROT_MTE support to mmap() and mprotect() Catalin Marinas
2020-05-27 18:57 ` Peter Collingbourne
2020-05-28 9:14 ` Catalin Marinas
2020-05-28 11:05 ` Szabolcs Nagy
2020-05-28 16:34 ` Catalin Marinas
2020-05-28 18:35 ` Evgenii Stepanov
2020-05-29 11:19 ` Catalin Marinas
2020-06-01 8:55 ` Dave Martin
2020-06-01 14:45 ` Catalin Marinas
2020-06-01 15:04 ` Dave Martin
2020-05-15 17:15 ` [PATCH v4 12/26] mm: Introduce arch_validate_flags() Catalin Marinas
2020-05-15 17:15 ` [PATCH v4 13/26] arm64: mte: Validate the PROT_MTE request via arch_validate_flags() Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 14/26] mm: Allow arm64 mmap(PROT_MTE) on RAM-based files Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 15/26] arm64: mte: Allow user control of the tag check mode via prctl() Catalin Marinas
2020-05-27 7:46 ` Will Deacon
2020-05-27 8:32 ` Dave Martin
2020-05-27 8:48 ` Will Deacon
2020-05-27 11:16 ` Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 16/26] arm64: mte: Allow user control of the generated random tags " Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 17/26] arm64: mte: Restore the GCR_EL1 register after a suspend Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 18/26] arm64: mte: Add PTRACE_{PEEK,POKE}MTETAGS support Catalin Marinas
2020-05-29 21:25 ` Luis Machado
2020-06-01 12:07 ` Catalin Marinas
2020-06-01 15:17 ` Luis Machado
2020-06-01 16:33 ` Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 19/26] fs: Handle intra-page faults in copy_mount_options() Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 20/26] mm: Add arch hooks for saving/restoring tags Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 21/26] arm64: mte: Enable swap of tagged pages Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 22/26] arm64: mte: Save tags when hibernating Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 23/26] arm64: mte: Check the DT memory nodes for MTE support Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 24/26] arm64: mte: Introduce early param to disable " Catalin Marinas
2020-05-18 11:26 ` Vladimir Murzin
2020-05-18 11:31 ` Will Deacon
2020-05-18 17:20 ` Catalin Marinas
2020-05-22 5:57 ` Patrick Daly [this message]
2020-05-22 10:37 ` Catalin Marinas
2020-05-27 2:11 ` Patrick Daly
2020-05-27 9:55 ` Will Deacon
2020-05-27 10:37 ` Szabolcs Nagy
2020-05-27 11:12 ` Catalin Marinas
2020-05-19 16:14 ` Catalin Marinas
2021-01-21 19:37 ` Andrey Konovalov
2021-01-22 2:03 ` Andrey Konovalov
2021-01-22 14:41 ` Catalin Marinas
2021-01-22 17:28 ` Andrey Konovalov
2020-05-15 17:16 ` [PATCH v4 25/26] arm64: mte: Kconfig entry Catalin Marinas
2020-05-15 17:16 ` [PATCH v4 26/26] arm64: mte: Add Memory Tagging Extension documentation Catalin Marinas
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