Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)
On 14.03.19 15:15, Juergen Gross wrote:
> On 14/03/2019 15:12, Julien Grall wrote:
>> Hi,
>>
>> On 3/14/19 8:37 AM, Juergen Gross wrote:
>>> On 12/03/2019 20:46, David Hildenbrand wrote:
On 12.03.19 19:23, David Hildenbrand wrote:
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(_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.
>>
>> Sure. I managed to get the console working with the patch suggested by
>> David. Feel free to add my tested-by if when you resend it as is.
>
> David, could you please send a proper patch with your Sob?
>
Yes, on it :)
Cheers!
>
> Juergen
>
--
Thanks,
David / dhildenb
Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)
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 +, 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 > 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 >>> 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
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 17:18, David Hildenbrand wrote: > On 12.03.19 18:14, Matthew Wilcox wrote: >> On Tue, Mar 12, 2019 at 05:05:39PM +, 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 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 >> 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
