From: Szabolcs Nagy <szabolcs.nagy@arm•com>
To: Will Deacon <will@kernel•org>
Cc: linux-arch@vger•kernel.org, nd@arm•com,
Vladimir Murzin <vladimir.murzin@arm•com>,
Patrick Daly <pdaly@codeaurora•org>,
Catalin Marinas <catalin.marinas@arm•com>,
Kevin Brodsky <kevin.brodsky@arm•com>,
linux-mm@kvack•org, Andrey Konovalov <andreyknvl@google•com>,
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: 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?
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next prev parent reply other threads:[~2020-05-27 10:38 UTC|newest]
Thread overview: 57+ 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
[not found] ` <CAFKCwri+X=de0gFrMZfA84dYmftSkcDc0DEvQ2JAmeOw2sLR=A@mail.gmail.com>
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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