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Message-ID: <CAPcyv4iPuRWSv_do_h8stU0-SiWxtKkQWvzBEU+78fDE6VffmA@mail.gmail.com>
Date: Tue, 29 Sep 2020 15:32:07 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Ingo Molnar <mingo@...hat.com>
Cc: Tony Luck <tony.luck@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Borislav Petkov <bp@...en8.de>,
stable <stable@...r.kernel.org>, X86 ML <x86@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Andy Lutomirski <luto@...nel.org>,
Paul Mackerras <paulus@...ba.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Erwin Tsaur <erwin.tsaur@...el.com>,
Michael Ellerman <mpe@...erman.id.au>,
Mikulas Patocka <mpatocka@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
0day robot <lkp@...el.com>,
linux-nvdimm <linux-nvdimm@...ts.01.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v9 0/2] Renovate memcpy_mcsafe with copy_mc_to_{user, kernel}
On Wed, Sep 23, 2020 at 10:00 AM Dan Williams <dan.j.williams@...el.com> wrote:
>
> Changes since v8 [1]:
> - Rebase on v5.9-rc6
>
> - Fix a performance regression in the x86 copy_mc_to_user()
> implementation that was duplicating copies in the "fragile" case.
>
> - Refreshed the cover letter.
>
> [1]: http://lore.kernel.org/r/159630255616.3143511.18110575960499749012.stgit@dwillia2-desk3.amr.corp.intel.com
>
Given that Linus was the primary source of review feedback on these
patches and a version of them have been soaking in -next with only a
minor conflict report with vfs.git for the entirety of the v5.9-rc
cycle (left there inadvertently while I was on leave), any concerns
with me sending this to Linus directly during the merge window?
>
> The motivations to go rework memcpy_mcsafe() are that the benefit of
> doing slow and careful copies is obviated on newer CPUs, and that the
> current opt-in list of cpus to instrument recovery is broken relative to
> those cpus. There is no need to keep an opt-in list up to date on an
> ongoing basis if pmem/dax operations are instrumented for recovery by
> default. With recovery enabled by default the old "mcsafe_key" opt-in to
> careful copying can be made a "fragile" opt-out. Where the "fragile"
> list takes steps to not consume poison across cachelines.
>
> The discussion with Linus made clear that the current "_mcsafe" suffix
> was imprecise to a fault. The operations that are needed by pmem/dax are
> to copy from a source address that might throw #MC to a destination that
> may write-fault, if it is a user page. So copy_to_user_mcsafe() becomes
> copy_mc_to_user() to indicate the separate precautions taken on source
> and destination. copy_mc_to_kernel() is introduced as a version that
> does not expect write-faults on the destination, but is still prepared
> to abort with an error code upon taking #MC.
>
> These patches have received a kbuild-robot build success notification
> across 114 configs, the rebase to v5.9-rc6 did not encounter any
> conflicts, and the merge with tip/master is conflict-free.
>
> ---
>
> Dan Williams (2):
> x86, powerpc: Rename memcpy_mcsafe() to copy_mc_to_{user,kernel}()
> x86/copy_mc: Introduce copy_mc_generic()
>
>
> arch/powerpc/Kconfig | 2
> arch/powerpc/include/asm/string.h | 2
> arch/powerpc/include/asm/uaccess.h | 40 +++--
> arch/powerpc/lib/Makefile | 2
> arch/powerpc/lib/copy_mc_64.S | 4
> arch/x86/Kconfig | 2
> arch/x86/Kconfig.debug | 2
> arch/x86/include/asm/copy_mc_test.h | 75 +++++++++
> arch/x86/include/asm/mcsafe_test.h | 75 ---------
> arch/x86/include/asm/string_64.h | 32 ----
> arch/x86/include/asm/uaccess.h | 21 +++
> arch/x86/include/asm/uaccess_64.h | 20 --
> arch/x86/kernel/cpu/mce/core.c | 8 -
> arch/x86/kernel/quirks.c | 9 -
> arch/x86/lib/Makefile | 1
> arch/x86/lib/copy_mc.c | 65 ++++++++
> arch/x86/lib/copy_mc_64.S | 165 ++++++++++++++++++++
> arch/x86/lib/memcpy_64.S | 115 --------------
> arch/x86/lib/usercopy_64.c | 21 ---
> drivers/md/dm-writecache.c | 15 +-
> drivers/nvdimm/claim.c | 2
> drivers/nvdimm/pmem.c | 6 -
> include/linux/string.h | 9 -
> include/linux/uaccess.h | 9 +
> include/linux/uio.h | 10 +
> lib/Kconfig | 7 +
> lib/iov_iter.c | 43 +++--
> tools/arch/x86/include/asm/mcsafe_test.h | 13 --
> tools/arch/x86/lib/memcpy_64.S | 115 --------------
> tools/objtool/check.c | 5 -
> tools/perf/bench/Build | 1
> tools/perf/bench/mem-memcpy-x86-64-lib.c | 24 ---
> tools/testing/nvdimm/test/nfit.c | 48 +++---
> .../testing/selftests/powerpc/copyloops/.gitignore | 2
> tools/testing/selftests/powerpc/copyloops/Makefile | 6 -
> .../selftests/powerpc/copyloops/copy_mc_64.S | 1
> .../selftests/powerpc/copyloops/memcpy_mcsafe_64.S | 1
> 37 files changed, 452 insertions(+), 526 deletions(-)
> rename arch/powerpc/lib/{memcpy_mcsafe_64.S => copy_mc_64.S} (98%)
> create mode 100644 arch/x86/include/asm/copy_mc_test.h
> delete mode 100644 arch/x86/include/asm/mcsafe_test.h
> create mode 100644 arch/x86/lib/copy_mc.c
> create mode 100644 arch/x86/lib/copy_mc_64.S
> delete mode 100644 tools/arch/x86/include/asm/mcsafe_test.h
> delete mode 100644 tools/perf/bench/mem-memcpy-x86-64-lib.c
> create mode 120000 tools/testing/selftests/powerpc/copyloops/copy_mc_64.S
> delete mode 120000 tools/testing/selftests/powerpc/copyloops/memcpy_mcsafe_64.S
>
> base-commit: ba4f184e126b751d1bffad5897f263108befc780
> _______________________________________________
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