On 08/31/2017 03:40 AM, Joonsoo Kim wrote: > On Tue, Aug 29, 2017 at 11:16:18AM +0200, Vlastimil Babka wrote: >> On 08/24/2017 08:36 AM, js1...@gmail.com wrote: >>> From: Joonsoo Kim <iamjoonsoo....@lge.com> >>> >>> 0. History >>> >>> This patchset is the follow-up of the discussion about the >>> "Introduce ZONE_CMA (v7)" [1]. Please reference it if more information >>> is needed. >>> >> >> [...] >> >>> >>> [1]: >>> lkml.kernel.org/r/1491880640-9944-1-git-send-email-iamjoonsoo....@lge.com >>> [2]: https://lkml.org/lkml/2014/10/15/623 >>> [3]: http://www.spinics.net/lists/linux-mm/msg100562.html >>> >>> Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com> >>> Acked-by: Vlastimil Babka <vba...@suse.cz> >> >> The previous version has introduced ZONE_CMA, so I would think switching >> to ZONE_MOVABLE is enough to drop previous reviews. Perhaps most of the >> code involved is basically the same, though? > > Yes, most of the code involved is the same. I considered to drop > previous review tags but most of the code and concept is the same so I > decide to keep review tags. I should mention it in cover-letter but I > forgot to mention it. Sorry about that. > >> Anyway I checked the current patch and did some basic tests with qemu, >> so you can keep my ack. > > Thanks! > >> >> BTW, if we dropped NR_FREE_CMA_PAGES, could we also drop MIGRATE_CMA and >> related hooks? Is that counter really that useful as it works right now? >> It will decrease both by CMA allocations (which has to be explicitly >> freed) and by movable allocations (which can be migrated). What if only >> CMA alloc/release touched it? > > I think that NR_FREE_CMA_PAGES would not be as useful as previous. We > can remove it. > > However, removing MIGRATE_CMA has a problem. There is an usecase to > check if the page comes from the CMA area or not. See > check_page_span() in mm/usercopy.c. I can implement it differently by > iterating whole CMA area and finding the match, but I'm not sure it's > performance effect. I guess that it would be marginal.
+CC Kees Cook Hmm, seems like this check is to make sure we don't copy from/to parts of kernel memory we're not supposed to? Then I believe checking that pages are in ZONE_MOVABLE should then give the same guarantees as MIGRATE_CMA. BTW the comment says "Reject if range is entirely either Reserved or CMA" but the code does the opposite thing. I assume the comment is wrong? > Anyway, I'd like not to cause any side-effect now. After patches are > settle down on mainline, I will try to remove them as you suggested. > > Thanks. > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majord...@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"d...@kvack.org";> em...@kvack.org </a> >
