From: Michal Hocko <mhocko@kernel.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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 17:27:36 +0200 [thread overview]
Message-ID: <20170518152736.GA18333@dhcp22.suse.cz> (raw)
In-Reply-To: <20170518151952.jzvz6aeelgx7ifmm@node.shutemov.name>
On Thu 18-05-17 18:19:52, Kirill A. Shutemov wrote:
> On Thu, May 18, 2017 at 01:43:59PM +0200, Michal Hocko wrote:
> > 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?
>
> Yes, I believe so.
>
> > 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?
>
> This would screw existing semantics of hint address -- "map here if
> free, please".
Well, the given address is just _hint_. We are still allowed to map to a
different place. And it is not specified whether the resulting mapping
is above or below that address. So I do not think it would screw the
existing semantic. Or do I miss something?
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-05-18 15:27 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
[not found] ` <20170518114359.GB25471-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2017-05-18 15:19 ` Kirill A. Shutemov
2017-05-18 15:27 ` Michal Hocko [this message]
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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