Date: Tue, 14 Nov 2017 19:44:30 -0800 From: Matthew Wilcox <willy@...radead.org> To: Dave Hansen <dave.hansen@...el.com> Cc: Tycho Andersen <tycho@...ker.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, kernel-hardening@...ts.openwall.com, Marco Benatto <marco.antonio.780@...il.com>, Juerg Haefliger <juerg.haefliger@...onical.com>, x86@...nel.org Subject: Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) On Mon, Nov 13, 2017 at 02:46:25PM -0800, Dave Hansen wrote: > On 11/13/2017 02:20 PM, Dave Hansen wrote: > > On 11/09/2017 05:09 PM, Tycho Andersen wrote: > >> which I guess is from the additional flags in grow_dev_page() somewhere down > >> the stack. Anyway... it seems this is a kernel allocation that's using > >> MIGRATE_MOVABLE, so perhaps we need some more fine tuned heuristic than just > >> all MOVABLE allocations are un-mapped via xpfo, and all the others are mapped. > >> > >> Do you have any ideas? > > > > It still has to do a kmap() or kmap_atomic() to be able to access it. I > > thought you hooked into that. Why isn't that path getting hit for these? > > Oh, this looks to be accessing data mapped by a buffer_head. It > (rudely) accesses data via: > > void set_bh_page(struct buffer_head *bh, > ... > bh->b_data = page_address(page) + offset; We don't need to kmap in order to access MOVABLE allocations. kmap is only needed for HIGHMEM allocations. So there's nothing wrong with ext4 or set_bh_page().
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