On 12/03/2019 17:18, David Hildenbrand wrote: > 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: >> >> 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. >> > Asking myself why anybody would want to map balloon inflated pages into > user space (this just sounds plain wrong but my understanding to what > XEN balloon driver does might be limited), but I assume the easy fix > would be to revert I suspect the bug here is that the balloon driver is (ab)used for a second purpose - to create a hole in pfn space to map some other bits of shared memory into. I think at the end of the day, what is needed is a struct page_info which looks like normal RAM, but the backing for which can be altered by hypercall to map other things. ~Andrew
