From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Patrick Daly <pdaly@codeaurora.org>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-arch@vger.kernel.org,
Vladimir Murzin <vladimir.murzin@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
Peter Collingbourne <pcc@google.com>,
linux-mm@kvack.org, Vincenzo Frascino <vincenzo.frascino@arm.com>,
Dave P Martin <Dave.Martin@arm.com>,
linux-arm-kernel@lists.infradead.org, nd@arm.com
Subject: Re: [PATCH v4 24/26] arm64: mte: Introduce early param to disable MTE support
Date: Wed, 27 May 2020 11:37:42 +0100 [thread overview]
Message-ID: <20200527103741.GB24512@arm.com> (raw)
In-Reply-To: <20200527095504.GB11111@willie-the-truck>
The 05/27/2020 10:55, Will Deacon wrote:
> On Tue, May 26, 2020 at 07:11:53PM -0700, Patrick Daly wrote:
> > On Fri, May 22, 2020 at 11:37:15AM +0100, Catalin Marinas wrote:
> > > The actual question here is what the on/off behaviour is needed for. We
> > > can figure out the best mechanism for this once we know what we want to
> > > achieve. My wild guess above was performance analysis but that can be
> > > toggled by either kernel boot parameter or run-time sysctl (or just the
> > > Kconfig option).
> > >
> > > If it is about forcing user space not to use MTE, we may look into some
> > > other sysctl controls (we already have one for the tagged address ABI).
> >
> > We want to allow the end user to be able to easily "opt out" of MTE in favour
> > of better power, perf and battery life.
>
> Who is "the end user" in this case?
>
> If MTE is bad enough for power, performance and battery life that we need a
> kill switch, then perhaps we shouldn't enable it by default and the few
> people that want to use it can build a kernel with it enabled. However, then
> I don't really see what MTE buys you over the existing KASAN implementations.
>
> I thought the general idea was that you could run in the (cheap) "async"
> mode, and then re-run in the more expensive "sync" mode to further diagnose
> any failures. That model seems to work well with these patches, since
> reporting is disabled by default. Are you saying that there is a
> significant penalty incurred even when reporting is not enabled?
>
> Anyway, we don't offer global runtime/cmdline switches for the vast majority
> of other architectural features -- instead, we choose a sensible default,
> and I think we should do the same here.
i would not expect mte overhead if userspace processes
don't map anything with PROT_MTE and don't enable tag
checking with prctl. (i.e. userspace runtimes can "opt
out" of mte for better power, perf and battery)
is that not the case?
next prev parent reply other threads:[~2020-05-27 10:38 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
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 [this message]
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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