Re: [PATCH 10/10] powerpc: remove address space overrides using set_fs()

[Christophe Leroy]

Le 02/09/2020 à 15:13, David Laight a écrit :
> From: Christoph Hellwig
> > Sent: 02 September 2020 13:37
> >
> > 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?
>
> Is TASK_SIZE_MASK defined such that you can do:
>
> 	return (addr | size) < TASK_SIZE_MAX) || !size;

TASK_SIZE_MAX will usually be 0xc0000000

With:
addr = 0x80000000;
size = 0x80000000;

I expect it to fail ....

With the formula you propose it will succeed, won't it ?

Christophe