From: David Laight <David.Laight@ACULAB.COM>
To: 'Arnd Bergmann' <arnd@arndb.de>,
Jisheng Zhang <jszhang@kernel.org>,
Andreas Schwab <schwab@suse.de>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
"linux-riscv@lists.infradead.org"
<linux-riscv@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 2/4] riscv: uaccess: use input constraints for ptr of __put_user
Date: Fri, 28 Jun 2024 15:36:17 +0000 [thread overview]
Message-ID: <b4d15c17ed684f5ab3cf89fda9f73618@AcuMS.aculab.com> (raw)
In-Reply-To: <dcf9574a-0f1b-4131-befd-39f47d4f9002@app.fastmail.com>
From: Arnd Bergmann
> Sent: 26 June 2024 15:25
...
> If you just copy from the arm64 version that uses an
> "r"(address) constraint instead of the "m"(*address)
> version, it should be fine for any user space access.
Arm certainly has 'reg+offset' addressing and I'd have thought
the RISC-V would have it as well.
I'd guess that the compiler also knows when the offset is too big.
Probably noticeable when code is accessing structures in user memory.
OTOH I can't remember if "m" implies a memory clobber?
For user copies the memory clobber isn't needed and not having it
may well allow better instruction scheduling.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2024-06-28 15:36 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-25 4:04 [PATCH 0/4] riscv: uaccess: optimizations Jisheng Zhang
2024-06-25 4:04 ` [PATCH 1/4] riscv: implement user_access_begin and families Jisheng Zhang
2024-06-26 23:38 ` Cyril Bur
2024-06-25 4:04 ` [PATCH 2/4] riscv: uaccess: use input constraints for ptr of __put_user Jisheng Zhang
2024-06-25 5:54 ` Arnd Bergmann
2024-06-26 12:32 ` Jisheng Zhang
2024-06-26 12:49 ` Jisheng Zhang
2024-06-26 13:18 ` Jisheng Zhang
2024-06-26 13:35 ` Andreas Schwab
2024-06-26 13:54 ` Jisheng Zhang
2024-06-26 13:12 ` Andreas Schwab
2024-06-26 13:12 ` Jisheng Zhang
2024-06-26 14:25 ` Arnd Bergmann
2024-06-26 16:02 ` Jisheng Zhang
2024-06-27 6:46 ` Arnd Bergmann
2024-06-28 15:36 ` David Laight [this message]
2024-06-25 4:04 ` [PATCH 3/4] riscv: uaccess: use 'asm goto' for put_user() Jisheng Zhang
2024-07-05 2:22 ` kernel test robot
2024-07-06 0:02 ` kernel test robot
2024-06-25 4:05 ` [PATCH 4/4] riscv: uaccess: use 'asm goto output' for get_user Jisheng Zhang
2024-07-05 4:13 ` kernel test robot
2024-06-25 7:21 ` [PATCH 0/4] riscv: uaccess: optimizations Arnd Bergmann
2024-06-25 18:12 ` Linus Torvalds
2024-06-26 13:04 ` Jisheng Zhang
2024-06-30 16:59 ` Linus Torvalds
2024-07-05 11:25 ` Will Deacon
2024-07-05 17:58 ` Linus Torvalds
2024-07-08 13:52 ` Will Deacon
2024-07-08 15:30 ` Mark Rutland
2024-07-23 14:16 ` Will Deacon
2024-07-08 15:21 ` Mark Rutland
2024-07-24 22:57 ` Palmer Dabbelt
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