xen/balloon: Fix mapping PG_offline pages to user space

PATCH Applied David Hildenbrand 2 participants 5 messages Mar 14, 2019 – Mar 15, 2019

Subsystems (2)

Memory management Xen hypervisor interface

lore

Share & tools

lore

David Hildenbrand

author

2019-03-14 16:03 UTC #0 lore raw

PATCH v2 1/1 xen/balloon: Fix mapping PG_offline pages to user space

The XEN balloon driver - in contrast to other balloon drivers - allows to map some inflated pages to user space. Such pages are allocated via alloc_xenballooned_pages() and freed via free_xenballooned_pages(). The pfn space of these allocated pages is used to map other things by the hypervisor using hypercalls.

Pages marked with PG_offline must never be mapped to user space (as this page type uses the mapcount field of struct pages).

So what we can do is, clear/set PG_offline when allocating/freeing an inflated pages. This way, most inflated pages can be excluded by dumping tools and the "reused for other purpose" balloon pages are correctly not marked as PG_offline.

Fixes 77c4adf6a6df (xen/balloon: mark inflated pages PG_offline)

Reported-by Julien Grall <[email protected]>

Tested-by Julien Grall <[email protected]>

Signed-off-by David Hildenbrand <[email protected]>

---

v1 -> v2:
- Readd the braces dropped by accident :)

 drivers/xen/balloon.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

drivers/xen/balloon.c +4 -1

index 39b229f9e256..d37dd5bb7a8f 100644
@@ -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;

Signature · 1 line

2.17.2

Juergen Gross

maintainer Reviewed-by on v2 1/1

2019-03-14 16:05 UTC #1 lore raw

Quoted 14 lines · David Hildenbrand

The XEN balloon driver - in contrast to other balloon drivers - allows to map some inflated pages to user space. Such pages are allocated via alloc_xenballooned_pages() and freed via free_xenballooned_pages(). The pfn space of these allocated pages is used to map other things by the hypervisor using hypercalls.
Pages marked with PG_offline must never be mapped to user space (as this page type uses the mapcount field of struct pages).
So what we can do is, clear/set PG_offline when allocating/freeing an inflated pages. This way, most inflated pages can be excluded by dumping tools and the "reused for other purpose" balloon pages are correctly not marked as PG_offline.

Quoted 4 lines

Fixes 77c4adf6a6df (xen/balloon: mark inflated pages PG_offline)
Reported-by Julien Grall <[email protected]>
Tested-by Julien Grall <[email protected]>
Signed-off-by David Hildenbrand <[email protected]>

Reviewed-by Juergen Gross <[email protected]>

Juergen

Juergen Gross

maintainer Reviewed-by on v2 1/1

2019-03-14 16:05 UTC #2 lore raw

In reply to David Hildenbrand

Quoted 14 lines · David Hildenbrand

The XEN balloon driver - in contrast to other balloon drivers - allows to map some inflated pages to user space. Such pages are allocated via alloc_xenballooned_pages() and freed via free_xenballooned_pages(). The pfn space of these allocated pages is used to map other things by the hypervisor using hypercalls.
Pages marked with PG_offline must never be mapped to user space (as this page type uses the mapcount field of struct pages).
So what we can do is, clear/set PG_offline when allocating/freeing an inflated pages. This way, most inflated pages can be excluded by dumping tools and the "reused for other purpose" balloon pages are correctly not marked as PG_offline.

Quoted 4 lines

Fixes 77c4adf6a6df (xen/balloon: mark inflated pages PG_offline)
Reported-by Julien Grall <[email protected]>
Tested-by Julien Grall <[email protected]>
Signed-off-by David Hildenbrand <[email protected]>

Reviewed-by Juergen Gross <[email protected]>

Juergen

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Xen-devel mailing list
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Juergen Gross

maintainer Applied

2019-03-15 14:53 UTC #3 lore raw

In reply to David Hildenbrand

Quoted 14 lines · David Hildenbrand

The XEN balloon driver - in contrast to other balloon drivers - allows to map some inflated pages to user space. Such pages are allocated via alloc_xenballooned_pages() and freed via free_xenballooned_pages(). The pfn space of these allocated pages is used to map other things by the hypervisor using hypercalls.
Pages marked with PG_offline must never be mapped to user space (as this page type uses the mapcount field of struct pages).
So what we can do is, clear/set PG_offline when allocating/freeing an inflated pages. This way, most inflated pages can be excluded by dumping tools and the "reused for other purpose" balloon pages are correctly not marked as PG_offline.

Quoted 4 lines

Fixes 77c4adf6a6df (xen/balloon: mark inflated pages PG_offline)
Reported-by Julien Grall <[email protected]>
Tested-by Julien Grall <[email protected]>
Signed-off-by David Hildenbrand <[email protected]>

Pushed to xen/tip.git for-linus-5.1b

Juergen

Juergen Gross

maintainer Applied

2019-03-15 14:53 UTC #4 lore raw

In reply to David Hildenbrand

Quoted 14 lines · David Hildenbrand

The XEN balloon driver - in contrast to other balloon drivers - allows to map some inflated pages to user space. Such pages are allocated via alloc_xenballooned_pages() and freed via free_xenballooned_pages(). The pfn space of these allocated pages is used to map other things by the hypervisor using hypercalls.
Pages marked with PG_offline must never be mapped to user space (as this page type uses the mapcount field of struct pages).
So what we can do is, clear/set PG_offline when allocating/freeing an inflated pages. This way, most inflated pages can be excluded by dumping tools and the "reused for other purpose" balloon pages are correctly not marked as PG_offline.

Quoted 4 lines

Fixes 77c4adf6a6df (xen/balloon: mark inflated pages PG_offline)
Reported-by Julien Grall <[email protected]>
Tested-by Julien Grall <[email protected]>
Signed-off-by David Hildenbrand <[email protected]>

Pushed to xen/tip.git for-linus-5.1b

Juergen

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Xen-devel mailing list
[email protected]
https://lists.xenproject.org/mailman/listinfo/xen-devel