linux-kernel - Re: [PATCH] mm: Fix mmap MAP_POPULATE for DAX pmd mapping

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1449093339.9855.1.camel@hpe.com>
Date:	Wed, 02 Dec 2015 14:55:39 -0700
From:	Toshi Kani <toshi.kani@....com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	mauricio.porto@....com, Linux MM <linux-mm@...ck.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Fix mmap MAP_POPULATE for DAX pmd mapping

On Wed, 2015-12-02 at 12:54 -0800, Dan Williams wrote:
> On Wed, Dec 2, 2015 at 1:37 PM, Toshi Kani <toshi.kani@....com> wrote:
> > On Wed, 2015-12-02 at 11:57 -0800, Dan Williams wrote:
> [..]
> > > The whole point of __get_user_page_fast() is to avoid the overhead of
> > > taking the mm semaphore to access the vma.  _PAGE_SPECIAL simply tells
> > > __get_user_pages_fast that it needs to fallback to the
> > > __get_user_pages slow path.
> > 
> > I see.  Then, I think gup_huge_pmd() can simply return 0 when !pfn_valid(),
> > instead of VM_BUG_ON.
> 
> Is pfn_valid() a reliable check?  It seems to be based on a max_pfn
> per node... what happens when pmem is located below that point.  I
> haven't been able to convince myself that we won't get false
> positives, but maybe I'm missing something.

I believe we use the version of pfn_valid() in linux/mmzone.h.

Thanks,
-Toshi
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/