[Xen-devel] [PATCH] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access

[Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>]

When __p2m_get_mem_access gets called, the p2m lock is already taken
by either get_page_from_gva or p2m_get_mem_access.

Possible code paths:
1)      -> get_page_from_gva
                -> p2m_mem_access_check_and_get_page
                        -> __p2m_get_mem_access
2)      -> p2m_get_mem_access
                -> __p2m_get_mem_access

In both cases if __p2m_get_mem_access subsequently gets to
call p2m_lookup (happens if !radix_tree_lookup(...)), a hypervisor
hang will occur, since p2m_lookup also spin-locks on the p2m lock.

This bug-fix simply replaces the p2m_lookup call from __p2m_get_mem_access
with a call to __p2m_lookup.

Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>
---
 xen/arch/arm/p2m.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 2190908..a9157e5 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -490,7 +490,7 @@ static int __p2m_get_mem_access(struct domain *d, gfn_t gfn,
          * No setting was found in the Radix tree. Check if the
          * entry exists in the page-tables.
          */
-        paddr_t maddr = p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
+        paddr_t maddr = __p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
         if ( INVALID_PADDR == maddr )
             return -ESRCH;
 
-- 
2.5.0


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