Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits

[Kirill A. Shutemov]

On Fri, Mar 24, 2017 at 02:44:10PM +0530, Aneesh Kumar K.V wrote:
> 
> 
> On Friday 24 March 2017 02:34 PM, Kirill A. Shutemov wrote:
> > On Mon, Mar 20, 2017 at 10:40:20AM +0530, Aneesh Kumar K.V wrote:
> > > "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> writes:
> > >  @@ -168,6 +182,10 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> > > >  	unsigned long addr = addr0;
> > > >  	struct vm_unmapped_area_info info;
> > > > 
> > > > +	addr = mpx_unmapped_area_check(addr, len, flags);
> > > > +	if (IS_ERR_VALUE(addr))
> > > > +		return addr;
> > > > +
> > > >  	/* requested length too big for entire address space */
> > > >  	if (len > TASK_SIZE)
> > > >  		return -ENOMEM;
> > > > @@ -192,6 +210,14 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> > > >  	info.length = len;
> > > >  	info.low_limit = PAGE_SIZE;
> > > >  	info.high_limit = mm->mmap_base;
> > > > +
> > > > +	/*
> > > > +	 * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area
> > > > +	 * in the full address space.
> > > > +	 */
> > > > +	if (addr > DEFAULT_MAP_WINDOW)
> > > > +		info.high_limit += TASK_SIZE - DEFAULT_MAP_WINDOW;
> > > > +
> > > 
> > > Is this ok for 32 bit application ?
> > 
> > DEFAULT_MAP_WINDOW is equal to TASK_SIZE on 32-bit, so it's nop and will
> > be compile out.
> > 
> 
> That is not about CONFIG_X86_32 but about 32 bit application on a 64 bit
> kernel. I guess we will never find addr > DEFAULT_MAP_WINDOW with
> a 32 bit app ?

I have local change to avoid this within 32-bit syscall, but I'll need to
recheck everthing.

-- 
 Kirill A. Shutemov