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

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Message-ID: <4500d8d9-7318-4505-6086-2d2dc41f3866@csgroup.eu>
Date:   Sat, 5 Sep 2020 09:16:06 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     David Laight <David.Laight@...LAB.COM>,
        'Alexey Dobriyan' <adobriyan@...il.com>,
        Ingo Molnar <mingo@...nel.org>
Cc:     "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Kees Cook <keescook@...omium.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: remove the last set_fs() in common code, and remove it for x86
 and powerpc v3



Le 04/09/2020 à 23:01, David Laight a écrit :
> 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.
> 

Intel added registers FS and GS in the i386

Christophe