Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)

[Juergen Gross]

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)
>>> ÂÂÂÂÂÂÂÂ while (pgno < nr_pages) {
>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ page = balloon_retrieve(true);
>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (page) {
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ __ClearPageOffline(page);
>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ pages[pgno++] = page;
>>> Â #ifdef CONFIG_XEN_HAVE_PVMMU
>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ /*
>>> @@ -645,8 +646,10 @@ void free_xenballooned_pages(int nr_pages, struct
>>> page **pages)
>>> ÂÂÂÂÂÂÂÂ mutex_lock(&balloon_mutex);
>>>
>>> ÂÂÂÂÂÂÂÂ for (i = 0; i < nr_pages; i++) {
>>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (pages[i])
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (pages[i]) {
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ __SetPageOffline(pages[i]);
>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ balloon_append(pages[i]);
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ }
>>> ÂÂÂÂÂÂÂÂ }
>>>
>>> ÂÂÂÂÂÂÂÂ 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?


Juergen