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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Mark Hemment <markhemm@googlemail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	patrice.chotard@foss.st.com,
	Mikulas Patocka <mpatocka@redhat.com>,
	Lukas Czerner <lczerner@redhat.com>,
	Christoph Hellwig <hch@lst.de>,
	"Darrick J. Wong" <djwong@kernel.org>,
	Chuck Lever <chuck.lever@oracle.com>,
	Hugh Dickins <hughd@google.com>,
	patches@lists.linux.dev, Linux-MM <linux-mm@kvack.org>,
	mm-commits@vger.kernel.org, Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH] x86/clear_user: Make it faster
Date: Tue, 24 May 2022 09:51:56 -0700	[thread overview]
Message-ID: <CAHk-=wiJ9xqFrdDJtUD3oc1kCxYcVjLi5BjBY-3NVHgYxYb_HA@mail.gmail.com> (raw)
In-Reply-To: <YozQZMyQ0NDdD8cH@zn.tnic>

On Tue, May 24, 2022 at 5:32 AM Borislav Petkov <bp@alien8.de> wrote:
>
> finally a somewhat final version, lightly tested.

I can't find anything wrong with this, but who knows what
patch-blindness I have from looking at a few different versions of it.
Maybe my eyes just skim over it now.

I do note that the clearing of %rax here:

> +.Lerms_exit:
> +       xorl %eax,%eax
> +       RET

seems to be unnecessary, since %rax is never modified in the path
leading to this. But maybe just as well just for consistency with the
cases where it *is* used as a temporary.

And I still suspect that "copy_to_user()" is *much* more interesting
than "clear_user()", but I guess we can't inline it anyway due to all
the other overhead (ie access_ok() and stac/clac).

And for a plain "call memcpy/memset", we'd need compiler help to do
this (at a minimum, we'd have to have the compiler use the 'rep
movs/stos' register logic, and then we could patch things in place
afterwards, with objtool creating the alternatives section or
something).

                    Linus

  reply	other threads:[~2022-05-24 16:52 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-15  2:12 incoming Andrew Morton
2022-04-15  2:13 ` [patch 01/14] MAINTAINERS: Broadcom internal lists aren't maintainers Andrew Morton
2022-04-15  2:13 ` [patch 02/14] tmpfs: fix regressions from wider use of ZERO_PAGE Andrew Morton
2022-04-15 22:10   ` Linus Torvalds
2022-04-15 22:21     ` Matthew Wilcox
2022-04-15 22:41     ` Hugh Dickins
2022-04-16  6:36     ` Borislav Petkov
2022-04-16 14:07       ` Mark Hemment
2022-04-16 17:28         ` Borislav Petkov
2022-04-16 17:42           ` Linus Torvalds
2022-04-16 21:15             ` Borislav Petkov
2022-04-17 19:41               ` Borislav Petkov
2022-04-17 20:56                 ` Linus Torvalds
2022-04-18 10:15                   ` Borislav Petkov
2022-04-18 17:10                     ` Linus Torvalds
2022-04-19  9:17                       ` Borislav Petkov
2022-04-19 16:41                         ` Linus Torvalds
2022-04-19 17:48                           ` Borislav Petkov
2022-04-21 15:06                             ` Borislav Petkov
2022-04-21 16:50                               ` Linus Torvalds
2022-04-21 17:22                                 ` Linus Torvalds
2022-04-24 19:37                                   ` Borislav Petkov
2022-04-24 19:54                                     ` Linus Torvalds
2022-04-24 20:24                                       ` Linus Torvalds
2022-04-27  0:14                                       ` Borislav Petkov
2022-04-27  1:29                                         ` Linus Torvalds
2022-04-27 10:41                                           ` Borislav Petkov
2022-04-27 16:00                                             ` Linus Torvalds
2022-05-04 18:56                                               ` Borislav Petkov
2022-05-04 19:22                                                 ` Linus Torvalds
2022-05-04 20:18                                                   ` Borislav Petkov
2022-05-04 20:40                                                     ` Linus Torvalds
2022-05-04 21:01                                                       ` Borislav Petkov
2022-05-04 21:09                                                         ` Linus Torvalds
2022-05-10  9:31                                                           ` clear_user (was: [patch 02/14] tmpfs: fix regressions from wider use of ZERO_PAGE) Borislav Petkov
2022-05-10 17:17                                                             ` Linus Torvalds
2022-05-10 17:28                                                             ` Linus Torvalds
2022-05-10 18:10                                                               ` Borislav Petkov
2022-05-10 18:57                                                                 ` Borislav Petkov
2022-05-24 12:32                                                                   ` [PATCH] x86/clear_user: Make it faster Borislav Petkov
2022-05-24 16:51                                                                     ` Linus Torvalds [this message]
2022-05-24 17:30                                                                       ` Borislav Petkov
2022-05-25 12:11                                                                     ` Mark Hemment
2022-05-27 11:28                                                                       ` Borislav Petkov
2022-05-27 11:10                                                                     ` Ingo Molnar
2022-06-22 14:21                                                                     ` Borislav Petkov
2022-06-22 15:06                                                                       ` Linus Torvalds
2022-06-22 20:14                                                                         ` Borislav Petkov
2022-06-22 21:07                                                                           ` Linus Torvalds
2022-06-23  9:41                                                                             ` Borislav Petkov
2022-07-05 17:01                                                                               ` [PATCH -final] " Borislav Petkov
2022-07-06  9:24                                                                                 ` Alexey Dobriyan
2022-07-11 10:33                                                                                   ` Borislav Petkov
2022-07-12 12:32                                                                                     ` Alexey Dobriyan
2022-08-06 12:49                                                                                       ` Borislav Petkov
2022-04-15  2:13 ` [patch 03/14] mm/secretmem: fix panic when growing a memfd_secret Andrew Morton
2022-04-15  2:13 ` [patch 04/14] irq_work: use kasan_record_aux_stack_noalloc() record callstack Andrew Morton
2022-04-15  2:13 ` [patch 05/14] kasan: fix hw tags enablement when KUNIT tests are disabled Andrew Morton
2022-04-15  2:13 ` [patch 06/14] mm, kfence: support kmem_dump_obj() for KFENCE objects Andrew Morton
2022-04-15  2:13 ` [patch 07/14] mm, page_alloc: fix build_zonerefs_node() Andrew Morton
2022-04-15  2:13 ` [patch 08/14] mm: fix unexpected zeroed page mapping with zram swap Andrew Morton
2022-04-15  2:13 ` [patch 09/14] mm: compaction: fix compiler warning when CONFIG_COMPACTION=n Andrew Morton
2022-04-15  2:13 ` [patch 10/14] hugetlb: do not demote poisoned hugetlb pages Andrew Morton
2022-04-15  2:13 ` [patch 11/14] revert "fs/binfmt_elf: fix PT_LOAD p_align values for loaders" Andrew Morton
2022-04-15  2:13 ` [patch 12/14] revert "fs/binfmt_elf: use PT_LOAD p_align values for static PIE" Andrew Morton
2022-04-15  2:14 ` [patch 13/14] mm/vmalloc: fix spinning drain_vmap_work after reading from /proc/vmcore Andrew Morton
2022-04-15  2:14 ` [patch 14/14] mm: kmemleak: take a full lowmem check in kmemleak_*_phys() Andrew Morton

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