From: Yury Norov <ynorov@nvidia.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Christophe Leroy (CS GROUP)" <chleroy@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Laight <david.laight.linux@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
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Subject: Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()
Date: Mon, 27 Apr 2026 18:30:16 -0400 [thread overview]
Message-ID: <ae_jeJLlVWjJ4sOY@yury> (raw)
In-Reply-To: <CAHk-=wgPrLy0FR3sEWBYQuNAac1axDASYMnTuPuxEU0WytzL7w@mail.gmail.com>
On Mon, Apr 27, 2026 at 02:52:05PM -0700, Linus Torvalds wrote:
> On Mon, 27 Apr 2026 at 12:19, Yury Norov <ynorov@nvidia.com> wrote:
> >
> > This is what Linus said when added x86 implementation for copy_from_user()
> > in c512c69187197:
>
> Note that some things have happily changed in the six+ years since...
>
> > That's partly because we have no current users of it, but also partly
> > because the copy_from_user() case is slightly different and cannot
> > efficiently be implemented in terms of a unsafe_get_user() loop (because
> > gcc can't do asm goto with outputs).
>
> now everybody can do asm goto with outputs.
>
> Yes, it's disabled on older versions, so it's not *always* available,
> but all modern versions do it. And if you care about performance, you
> won't be using an old compiler.
The minimal GCC version is 8.1, and asm goto with outputs is supported
since GCC-11. That would brake the build, if we just switch to using it
without "CC_IS_GCC && (GCC_VERSION >= 110100)" guard.
Is it worth to maintain 2 version of the function? I don't know...
Thanks,
Yury
next prev parent reply other threads:[~2026-04-27 22:30 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-27 17:13 [RFC PATCH v1 0/9] uaccess: Convert small fixed size copy_{to/from}_user() to scoped user access Christophe Leroy (CS GROUP)
2026-04-27 17:13 ` [RFC PATCH v1 1/9] uaccess: Split check_zeroed_user() out of usercopy.c Christophe Leroy (CS GROUP)
2026-04-27 17:13 ` [RFC PATCH v1 2/9] uaccess: Convert INLINE_COPY_{TO/FROM}_USER to kconfig and reduce ifdefery Christophe Leroy (CS GROUP)
2026-04-27 18:39 ` Yury Norov
2026-04-27 20:39 ` Andrew Cooper
2026-04-27 20:47 ` Yury Norov
2026-04-27 17:13 ` [RFC PATCH v1 3/9] x86/umip: Be stricter in fixup_umip_exception() Christophe Leroy (CS GROUP)
2026-04-27 17:13 ` [RFC PATCH v1 4/9] uaccess: Introduce copy_{to/from}_user_partial() Christophe Leroy (CS GROUP)
2026-04-27 17:13 ` [RFC PATCH v1 5/9] uaccess: Switch to copy_{to/from}_user_partial() when relevant Christophe Leroy (CS GROUP)
2026-04-27 18:07 ` Alice Ryhl
2026-04-27 19:01 ` Linus Torvalds
2026-04-27 21:29 ` David Laight
2026-04-27 21:39 ` Linus Torvalds
2026-04-27 17:13 ` [RFC PATCH v1 6/9] uaccess: Change copy_{to/from}_user to return -EFAULT Christophe Leroy (CS GROUP)
2026-04-27 17:13 ` [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user() Christophe Leroy (CS GROUP)
2026-04-27 17:58 ` Yury Norov
2026-04-27 18:20 ` Christophe Leroy (CS GROUP)
2026-04-27 19:19 ` Yury Norov
2026-04-27 21:52 ` Linus Torvalds
2026-04-27 22:30 ` Yury Norov [this message]
2026-04-27 17:13 ` [RFC PATCH v1 8/9] arm64: " Christophe Leroy (CS GROUP)
2026-04-27 17:13 ` [RFC PATCH v1 9/9] uaccess: Convert small fixed size copy_{to/from}_user() to scoped user access Christophe Leroy (CS GROUP)
2026-04-27 20:12 ` Yury Norov
2026-04-27 19:01 ` [RFC PATCH v1 0/9] " Helge Deller
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