linux-kernel - RE: remove the last set_fs() in common code, and remove it for x86 and powerpc v3

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Date:   Fri, 4 Sep 2020 21:01:06 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alexey Dobriyan' <adobriyan@...il.com>,
        Ingo Molnar <mingo@...nel.org>
CC:     Christoph Hellwig <hch@....de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        "x86@...nel.org" <x86@...nel.org>,
        "Luis Chamberlain" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: RE: remove the last set_fs() in common code, and remove it for x86
 and powerpc v3

From: Alexey Dobriyan
> Sent: 04 September 2020 18:58
> 
> On Fri, Sep 04, 2020 at 08:00:24AM +0200, Ingo Molnar wrote:
> > * Christoph Hellwig <hch@....de> wrote:
> > > this series removes the last set_fs() used to force a kernel address
> > > space for the uaccess code in the kernel read/write/splice code, and then
> > > stops implementing the address space overrides entirely for x86 and
> > > powerpc.
> >
> > Cool! For the x86 bits:
> >
> >   Acked-by: Ingo Molnar <mingo@...nel.org>
> 
> set_fs() is older than some kernel hackers!
> 
> 	$ cd linux-0.11/
> 	$ find . -type f -name '*.h' | xargs grep -e set_fs -w -n -A3
> 	./include/asm/segment.h:61:extern inline void set_fs(unsigned long val)
> 	./include/asm/segment.h-62-{
> 	./include/asm/segment.h-63-     __asm__("mov %0,%%fs"::"a" ((unsigned short) val));
> 	./include/asm/segment.h-64-}

What is this strange %fs register you are talking about.
Figure 2-4 only has CS, DS, SS and ES.

	David

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