From: Christoph Hellwig <hch@lst.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>,
the arch/x86 maintainers <x86@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Masami Hiramatsu <mhiramat@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-parisc@vger.kernel.org,
linux-um <linux-um@lists.infradead.org>,
Netdev <netdev@vger.kernel.org>,
bpf@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 14/18] maccess: allow architectures to provide kernel probing directly
Date: Wed, 13 May 2020 21:54:56 +0200 [thread overview]
Message-ID: <20200513195456.GA31096@lst.de> (raw)
In-Reply-To: <CAHk-=whtGLxezkdMP6+859LFDgb++6dgYa6Vrc=zJ9+GB7UMFQ@mail.gmail.com>
On Wed, May 13, 2020 at 12:48:54PM -0700, Linus Torvalds wrote:
> Looking at the current users of "probe_kernel_read()", it looks like
> it's almost mostly things that just want a single byte or word.
>
> It's not 100% that: we definitely do several things that want the
> "copy" semantics vs the "get" semantics: on the x86 side we have
> CALL_INSN_SIZE and MAX_INSN_SIZE, and the ldttss_desc.
>
> But the bulk of them do seem to be a single value.
>
> I don't know if performance really matters here, but to me the whole
> "most users seem to want to read a single value" is what makes me
> think that maybe that should be the primary model, rather than have
> the copy model be the primary one and then we implement the single
> value case (badly) with a copy.
>
> It probably doesn't matter that much. I certainly wouldn't hold this
> series up over it - it can be a future thing.
I can make the get_kernel_nofault implementation suck a little less :)
Note that the arch helper (we could call it unsafe_get_kernel_nofault)
we still need to have a pagefault_disable / pagefault_enable pair
around the calls. So maybe keep the get_kernel_nofault interface
as-is (without the goto label), and prepare the arch helpers for
being used similar to unsafe_get_user once all architectures are
converted. And I can throw in a few patches to convert callers
from the copy semantics to the get semantics.
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-parisc@vger.kernel.org,
Daniel Borkmann <daniel@iogearbox.net>,
Netdev <netdev@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
linux-um <linux-um@lists.infradead.org>,
Alexei Starovoitov <ast@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
bpf@vger.kernel.org, Masami Hiramatsu <mhiramat@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 14/18] maccess: allow architectures to provide kernel probing directly
Date: Wed, 13 May 2020 21:54:56 +0200 [thread overview]
Message-ID: <20200513195456.GA31096@lst.de> (raw)
In-Reply-To: <CAHk-=whtGLxezkdMP6+859LFDgb++6dgYa6Vrc=zJ9+GB7UMFQ@mail.gmail.com>
On Wed, May 13, 2020 at 12:48:54PM -0700, Linus Torvalds wrote:
> Looking at the current users of "probe_kernel_read()", it looks like
> it's almost mostly things that just want a single byte or word.
>
> It's not 100% that: we definitely do several things that want the
> "copy" semantics vs the "get" semantics: on the x86 side we have
> CALL_INSN_SIZE and MAX_INSN_SIZE, and the ldttss_desc.
>
> But the bulk of them do seem to be a single value.
>
> I don't know if performance really matters here, but to me the whole
> "most users seem to want to read a single value" is what makes me
> think that maybe that should be the primary model, rather than have
> the copy model be the primary one and then we implement the single
> value case (badly) with a copy.
>
> It probably doesn't matter that much. I certainly wouldn't hold this
> series up over it - it can be a future thing.
I can make the get_kernel_nofault implementation suck a little less :)
Note that the arch helper (we could call it unsafe_get_kernel_nofault)
we still need to have a pagefault_disable / pagefault_enable pair
around the calls. So maybe keep the get_kernel_nofault interface
as-is (without the goto label), and prepare the arch helpers for
being used similar to unsafe_get_user once all architectures are
converted. And I can throw in a few patches to convert callers
from the copy semantics to the get semantics.
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next prev parent reply other threads:[~2020-05-13 19:55 UTC|newest]
Thread overview: 100+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 16:00 clean up and streamline probe_kernel_* and friends v2 Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 01/18] maccess: unexport probe_kernel_write and probe_user_write Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 02/18] maccess: remove various unused weak aliases Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 03/18] maccess: remove duplicate kerneldoc comments Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 04/18] maccess: clarify " Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 05/18] maccess: update the top of file comment Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 06/18] maccess: rename strncpy_from_unsafe_user to strncpy_from_user_nofault Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 07/18] maccess: rename strncpy_from_unsafe_strict to strncpy_from_kernel_nofault Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 08/18] maccess: rename strnlen_unsafe_user to strnlen_user_nofault Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 09/18] maccess: remove probe_read_common and probe_write_common Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 10/18] maccess: unify the probe kernel arch hooks Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-14 1:13 ` Masami Hiramatsu
2020-05-14 1:13 ` Masami Hiramatsu
2020-05-19 5:46 ` Christoph Hellwig
2020-05-19 5:46 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 11/18] maccess: remove strncpy_from_unsafe Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 19:11 ` Linus Torvalds
2020-05-13 19:11 ` Linus Torvalds
2020-05-13 19:11 ` Linus Torvalds
2020-05-13 19:28 ` Christoph Hellwig
2020-05-13 19:28 ` Christoph Hellwig
2020-05-13 22:36 ` Daniel Borkmann
2020-05-13 22:36 ` Daniel Borkmann
2020-05-13 23:03 ` Linus Torvalds
2020-05-13 23:03 ` Linus Torvalds
2020-05-13 23:03 ` Linus Torvalds
2020-05-13 23:24 ` Daniel Borkmann
2020-05-13 23:24 ` Daniel Borkmann
2020-05-13 23:20 ` Masami Hiramatsu
2020-05-13 23:20 ` Masami Hiramatsu
2020-05-13 23:59 ` Linus Torvalds
2020-05-13 23:59 ` Linus Torvalds
2020-05-13 23:59 ` Linus Torvalds
2020-05-14 1:00 ` Masami Hiramatsu
2020-05-14 1:00 ` Masami Hiramatsu
2020-05-14 2:43 ` Linus Torvalds
2020-05-14 2:43 ` Linus Torvalds
2020-05-14 2:43 ` Linus Torvalds
2020-05-14 9:44 ` Masami Hiramatsu
2020-05-14 9:44 ` Masami Hiramatsu
2020-05-14 10:27 ` Daniel Borkmann
2020-05-14 10:27 ` Daniel Borkmann
2020-05-13 23:28 ` Al Viro
2020-05-13 23:28 ` Al Viro
2020-05-13 23:58 ` Daniel Borkmann
2020-05-13 23:58 ` Daniel Borkmann
2020-05-14 10:01 ` David Laight
2020-05-14 10:01 ` David Laight
2020-05-14 10:21 ` Daniel Borkmann
2020-05-14 10:21 ` Daniel Borkmann
2020-05-13 16:00 ` [PATCH 12/18] maccess: always use strict semantics for probe_kernel_read Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 13/18] maccess: move user access routines together Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 14/18] maccess: allow architectures to provide kernel probing directly Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 19:36 ` Linus Torvalds
2020-05-13 19:36 ` Linus Torvalds
2020-05-13 19:36 ` Linus Torvalds
2020-05-13 19:40 ` Christoph Hellwig
2020-05-13 19:40 ` Christoph Hellwig
2020-05-13 19:48 ` Linus Torvalds
2020-05-13 19:48 ` Linus Torvalds
2020-05-13 19:48 ` Linus Torvalds
2020-05-13 19:54 ` Christoph Hellwig [this message]
2020-05-13 19:54 ` Christoph Hellwig
2020-05-16 3:42 ` Masami Hiramatsu
2020-05-16 3:42 ` Masami Hiramatsu
2020-05-18 15:09 ` Christoph Hellwig
2020-05-18 15:09 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 15/18] x86: use non-set_fs based maccess routines Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 16/18] maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 16/18] maccess: rename probe_kernel_{read, write} to copy_{from, to}_kernel_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 17/18] maccess: rename probe_user_{read,write} to copy_{from,to}_user_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 17/18] maccess: rename probe_user_{read, write} to copy_{from, to}_user_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 18/18] maccess: rename probe_kernel_address to get_kernel_nofault Christoph Hellwig
2020-05-13 16:00 ` Christoph Hellwig
2020-05-13 19:37 ` clean up and streamline probe_kernel_* and friends v2 Linus Torvalds
2020-05-13 19:37 ` Linus Torvalds
2020-05-13 19:37 ` Linus Torvalds
2020-05-13 23:04 ` Daniel Borkmann
2020-05-13 23:04 ` Daniel Borkmann
2020-05-13 23:20 ` Linus Torvalds
2020-05-13 23:20 ` Linus Torvalds
2020-05-13 23:20 ` Linus Torvalds
2020-05-19 5:50 ` Christoph Hellwig
2020-05-19 5:50 ` Christoph Hellwig
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