[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)
On 12/03/2019 20:46, David Hildenbrand wrote: > On 12.03.19 19:23, David Hildenbrand wrote: >> 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) >> > > I guess something like this could do the trick if I understood it correctly: > > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c > index 39b229f9e256..d37dd5bb7a8f 100644 > --- a/drivers/xen/balloon.c > +++ b/drivers/xen/balloon.c > @@ -604,6 +604,7 @@ int alloc_xenballooned_pages(int nr_pages, struct > page **pages) > while (pgno < nr_pages) { > page = balloon_retrieve(true); > if (page) { > + __ClearPageOffline(page); > pages[pgno++] = page; > #ifdef CONFIG_XEN_HAVE_PVMMU > /* > @@ -645,8 +646,10 @@ void free_xenballooned_pages(int nr_pages, struct > page **pages) > mutex_lock(&balloon_mutex); > > for (i = 0; i < nr_pages; i++) { > - if (pages[i]) > + if (pages[i]) { > + __SetPageOffline(pages[i]); > balloon_append(pages[i]); > + } > } > > balloon_stats.target_unpopulated -= nr_pages; > > > At least this way, the pages allocated (and thus eventually mapped to > user space) would not be marked, but the other ones would remain marked > and could be excluded by makedumptool. > I think this patch should do the trick. Julien, could you give it a try? On x86 I can't reproduce your problem easily as dom0 is PV with plenty of unpopulated pages for grant memory not suffering from missing "offline" bit. Juergen _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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