From: Michal Hocko <mhocko@kernel.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Andi Kleen <ak@linux.intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Andy Lutomirski <luto@amacapital.net>,
Dan Williams <dan.j.williams@intel.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-api@vger.kernel.org
Subject: Re: [PATCHv5, REBASED 9/9] x86/mm: Allow to have userspace mappings above 47-bits
Date: Thu, 18 May 2017 13:43:59 +0200 [thread overview]
Message-ID: <20170518114359.GB25471@dhcp22.suse.cz> (raw)
In-Reply-To: <20170515121218.27610-10-kirill.shutemov@linux.intel.com>
On Mon 15-05-17 15:12:18, Kirill A. Shutemov wrote:
[...]
> @@ -195,6 +207,16 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
> info.length = len;
> info.low_limit = PAGE_SIZE;
> info.high_limit = get_mmap_base(0);
> +
> + /*
> + * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area
> + * in the full address space.
> + *
> + * !in_compat_syscall() check to avoid high addresses for x32.
> + */
> + if (addr > DEFAULT_MAP_WINDOW && !in_compat_syscall())
> + info.high_limit += TASK_SIZE_MAX - DEFAULT_MAP_WINDOW;
> +
> info.align_mask = 0;
> info.align_offset = pgoff << PAGE_SHIFT;
> if (filp) {
I have two questions/concerns here. The above assumes that any address above
1<<47 will use the _whole_ address space. Is this what we want? What
if somebody does mmap(1<<52, ...) because he wants to (ab)use 53+ bits
for some other purpose? Shouldn't we cap the high_limit by the given
address?
Another thing would be that
/* requesting a specific address */
if (addr) {
addr = PAGE_ALIGN(addr);
vma = find_vma(mm, addr);
if (TASK_SIZE - len >= addr &&
(!vma || addr + len <= vma->vm_start))
return addr;
}
would fail for mmap(-1UL, ...) which is good because we do want to
fallback to vm_unmapped_area and have randomized address which is
ensured by your info.high_limit += ... but that wouldn't work for
mmap(1<<N, ...) where N>47. So the first such mapping won't be
randomized while others will be. This is quite unexpected I would say.
So it should be documented at least or maybe we want to skip the above
shortcut for addr > DEFAULT_MAP_WINDOW altogether.
The patch looks sensible other than that.
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-05-18 11:43 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20170515121218.27610-1-kirill.shutemov@linux.intel.com>
2017-05-15 12:12 ` [PATCHv5, REBASED 9/9] x86/mm: Allow to have userspace mappings above 47-bits Kirill A. Shutemov
[not found] ` <20170515121218.27610-10-kirill.shutemov-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2017-05-15 14:49 ` kbuild test robot
[not found] ` <201705152204.F4FmHH4W%fengguang.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-05-15 19:48 ` Kirill A. Shutemov
2017-05-18 11:43 ` Michal Hocko [this message]
[not found] ` <20170518114359.GB25471-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2017-05-18 15:19 ` Kirill A. Shutemov
2017-05-18 15:27 ` Michal Hocko
2017-05-18 15:41 ` Kirill A. Shutemov
2017-05-18 15:50 ` Michal Hocko
2017-05-18 15:59 ` Michal Hocko
2017-05-18 16:22 ` Kirill A. Shutemov
[not found] ` <20170518162255.l55tm5qbmnvvsgba-sVvlyX1904swdBt8bTSxpkEMvNT87kid@public.gmane.org>
2017-05-18 17:13 ` Michal Hocko
[not found] ` <20170518171330.GA30148-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2017-05-18 17:51 ` Michal Hocko
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