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

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Message-ID: <20170324093019.ts7sljfg32kpajd2@node.shutemov.name>
Date:   Fri, 24 Mar 2017 12:30:19 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Michal Hocko <mhocko@...e.com>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above
 47-bits

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@...ux.intel.com> 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