linux-kernel - Re: [PATCH 10/10] powerpc: remove address space overrides using set

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Date:   Wed, 2 Sep 2020 17:17:34 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Christoph Hellwig <hch@....de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>, x86@...nel.org,
        linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/10] powerpc: remove address space overrides using
 set_fs()



Le 02/09/2020 à 14:36, Christoph Hellwig a écrit :
> On Wed, Sep 02, 2020 at 08:15:12AM +0200, Christophe Leroy wrote:
>>> -		return 0;
>>> -	return (size == 0 || size - 1 <= seg.seg - addr);
>>> +	if (addr >= TASK_SIZE_MAX)
>>> +		return false;
>>> +	if (size == 0)
>>> +		return false;
>>
>> __access_ok() was returning true when size == 0 up to now. Any reason to
>> return false now ?
> 
> No, this is accidental and broken.  Can you re-run your benchmark with
> this fixed?
> 

With this fix, I get

root@...ippro:~# time dd if=/dev/zero of=/dev/null count=1M
1048576+0 records in
1048576+0 records out
536870912 bytes (512.0MB) copied, 6.776327 seconds, 75.6MB/s
real    0m 6.78s
user    0m 1.64s
sys     0m 5.13s

That's still far from the 91.7MB/s I get with 5.9-rc2, but better than 
the 65.8MB/s I got yesterday with your series. Still some way to go thought.

Christophe