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From: Christoph Hellwig <hch@lst.de>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@lst.de>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH 3/8] asm-generic: fix unaligned access hamdling in raw_copy_{from,to}_user
Date: Sat, 5 Sep 2020 09:14:47 +0200	[thread overview]
Message-ID: <20200905071447.GA13228@lst.de> (raw)
In-Reply-To: <CAK8P3a1=udSEq8kpsmLk-b7ye0p=6eKTvBV74jBoGYmufL2oEw@mail.gmail.com>

On Fri, Sep 04, 2020 at 08:04:34PM +0200, Arnd Bergmann wrote:
> >         if (__builtin_constant_p(n)) {
> >                 switch(n) {
> >                 case 1:
> > -                       *(u8 *)to = *(u8 __force *)from;
> > +                       *(u8 *)to = get_unaligned((u8 __force *)from);
> >                         return 0;
> >                 case 2:
> > -                       *(u16 *)to = *(u16 __force *)from;
> > +                       *(u16 *)to = get_unaligned((u16 __force *)from);
> >                         return 0;
> 
> The change look correct and necessary, but I wonder if this could be done
> in a way that is a little easier on the compiler than the nested switch/case.
> 
> If I see it right, __put_user() and __get_user() can probably
> be reduced to a plain put_unaligned() and get_unaligned() here,
> which would simplify these a lot.
> 
> In turn it seems that the generic raw_copy_to_user() can just be the
> a plain memcpy(), IIRC the optimization for small sizes should also
> be done by modern compilers whenever they can.

Sure, I can look into that.

  reply	other threads:[~2020-09-05  7:14 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-04 16:52 remove set_fs for riscv Christoph Hellwig
2020-09-04 16:52 ` [PATCH 1/8] maccess: add a generic __{get,put}_kernel_nofault for nommu Christoph Hellwig
2020-09-04 16:52 ` [PATCH 2/8] uaccess: provide a generic TASK_SIZE_MAX definition Christoph Hellwig
2020-09-04 16:52 ` [PATCH 3/8] asm-generic: fix unaligned access hamdling in raw_copy_{from,to}_user Christoph Hellwig
2020-09-04 18:04   ` Arnd Bergmann
2020-09-05  7:14     ` Christoph Hellwig [this message]
2020-09-04 18:06   ` Al Viro
2020-09-04 22:35     ` Al Viro
2020-09-05 14:41       ` Al Viro
2020-09-07  8:07       ` Arnd Bergmann
2020-09-07 19:00   ` [PATCH 3/8] asm-generic: fix unaligned access hamdling in raw_copy_{from, to}_user Sean Anderson
2020-09-04 16:52 ` [PATCH 4/8] asm-generic: prepare uaccess.h for a set_fs-less world Christoph Hellwig
2020-09-04 16:52 ` [PATCH 5/8] riscv: use memcpy based uaccess for nommu again Christoph Hellwig
2020-09-04 16:52 ` [PATCH 6/8] riscv: refactor __get_user and __put_user Christoph Hellwig
2020-09-04 16:52 ` [PATCH 7/8] riscv: implement __get_kernel_nofault and __put_user_nofault Christoph Hellwig
2020-09-04 16:52 ` [PATCH 8/8] riscv: remove address space overrides using set_fs() Christoph Hellwig
2020-09-04 18:15 ` remove set_fs for riscv Arnd Bergmann
2020-09-05  7:17   ` Christoph Hellwig
2020-09-05 12:17     ` Arnd Bergmann
2020-09-06 22:14     ` Arnd Bergmann
2020-09-07  6:03       ` Christoph Hellwig
2020-09-07 14:58         ` Arnd Bergmann

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