On 12.03.19 19:02, Boris Ostrovsky wrote: > On 3/12/19 1:24 PM, Andrew Cooper wrote: >> 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 > > Yes. And its name is alloc_xenballooned_pages(). > Haven't had a look at the code yet, but would another temporary fix be to clear/set PG_offline when allocating/freeing a ballooned page? (assuming here that only such pages will be mapped to user space) -- Thanks, David / dhildenb
