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(). -boris > - 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
