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

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Date:   Fri, 24 Mar 2017 14:44:10 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
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 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 ?

-aneesh