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Date: Wed, 15 Nov 2017 15:18:02 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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        Nicholas Piggin <npiggin@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across
 DEFAULT_MAP_WINDOW border
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On Wed, 15 Nov 2017, Kirill A. Shutemov wrote:
> On Wed, Nov 15, 2017 at 12:39:40PM +0100, Thomas Gleixner wrote:
> > > I *think* we should be fine with checking unaligned 'addr'.
> > 
> > I think we should keep it consistent for the normal and the huge case and
> > just check aligned and be done with it.
> 
> Aligned 'addr'? Or 'len'? Both?
> 
> We would have problem with checking aligned addr. I steped it in hugetlb
> case:
> 
>   - User asks for mmap((1UL << 47) - PAGE_SIZE, 2 << 20, MAP_HUGETLB);
> 
>   - On 4-level paging machine this gives us invalid hint address as
>     'TASK_SIZE - len' is more than 'addr'. Goto get_unmapped_area.
> 
>   - On 5-level paging machine hint address gets rounded up to next 2MB
>     boundary that is exactly 1UL << 47 and we happily allocate from full
>     address space which may lead to trouble.

Ah, right because that ALIGN is using huge_page_size(h) and not PAGE_SIZE.