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



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(&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.

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.

Cheers,

--
Julien Grall

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