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memory: fix XENMEM_exchange error handling
assign_pages() can fail due to the domain getting killed in parallel,
which should not result in a hypervisor crash.
Also delete a redundant put_gfn() - all relevant paths leading to the
"fail" label already do this (and there are also paths where it was
plain wrong). All of the put_gfn()-s got introduced by 51032ca058
("Modify naming of queries into the p2m"), including the otherwise
unneeded initializer for k (with even a kind of misleading comment -
the compiler warning could actually have served as a hint that the use
is wrong).
This is XSA-159.
Reported-by: Julien Grall <julien.grall@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -334,7 +334,7 @@ static long memory_exchange(XEN_GUEST_HA
PAGE_LIST_HEAD(out_chunk_list);
unsigned long in_chunk_order, out_chunk_order;
xen_pfn_t gpfn, gmfn, mfn;
- unsigned long i, j, k = 0; /* gcc ... */
+ unsigned long i, j, k;
unsigned int memflags = 0;
long rc = 0;
struct domain *d;
@@ -572,11 +572,12 @@ static long memory_exchange(XEN_GUEST_HA
fail:
/* Reassign any input pages we managed to steal. */
while ( (page = page_list_remove_head(&in_chunk_list)) )
- {
- put_gfn(d, gmfn + k--);
if ( assign_pages(d, page, 0, MEMF_no_refcount) )
- BUG();
- }
+ {
+ BUG_ON(!d->is_dying);
+ if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
+ put_page(page);
+ }
dying:
rcu_unlock_domain(d);
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