On 12.03.19 18:14, Matthew Wilcox wrote: > On Tue, Mar 12, 2019 at 05:05:39PM +0000, Julien Grall wrote: >> On 3/12/19 3:59 PM, Julien Grall wrote: >>> It looks like all the arm test for linus [1] and next [2] tree >>> are now failing. x86 seems to be mostly ok. >>> >>> The bisector fingered the following commit: >>> >>> commit 0ee930e6cafa048c1925893d0ca89918b2814f2c >>> Author: Matthew Wilcox <willy@xxxxxxxxxxxxx> >>> Date: Tue Mar 5 15:46:06 2019 -0800 >>> >>> mm/memory.c: prevent mapping typed pages to userspace >>> Pages which use page_type must never be mapped to userspace as it would >>> destroy their page type. Add an explicit check for this instead of >>> assuming that kernel drivers always get this right. > > Oh good, it found a real problem. > >> It turns out the problem is because the balloon driver will call >> __SetPageOffline() on allocated page. Therefore the page has a type and >> vm_insert_pages will deny the insertion. >> >> My knowledge is quite limited in this area. So I am not sure how we can >> solve the problem. >> >> I would appreciate if someone could provide input of to fix the mapping. > > I don't know the balloon driver, so I don't know why it was doing this, > but what it was doing was Wrong and has been since 2014 with: Just to clarify on that point, XEN balloon does not use balloon compaction as far as I know (only virtio-balloon and as far as I know now also vmware balloon). Both of them don't map any such pages to user space, so it never was and isn't a problem. > > commit d6d86c0a7f8ddc5b38cf089222cb1d9540762dc2 > Author: Konstantin Khlebnikov <k.khlebnikov@xxxxxxxxxxx> > Date: Thu Oct 9 15:29:27 2014 -0700 > > mm/balloon_compaction: redesign ballooned pages management > > If ballooned pages are supposed to be mapped into userspace, you can't mark > them as ballooned pages using the mapcount field. > -- Thanks, David / dhildenb
