arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access

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.

Following Ian's suggestion, we also add an ASSERT to ensure that
the p2m lock is taken upon __p2m_get_mem_access entry.

Signed-off-by: Corneliu ZUZU <czuzu@bitdefender.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 21909082e40fe09974f3363c6af8719df06cf851..e8e6db4eb342faf8f222539c65e5114a5ecb60d8 100644 (file)
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -468,6 +468,8 @@ static int __p2m_get_mem_access(struct domain *d, gfn_t gfn,
 #undef ACCESS
     };
 
+    ASSERT(spin_is_locked(&p2m->lock));
+
     /* If no setting was ever set, just return rwx. */
     if ( !p2m->mem_access_enabled )
     {
@@ -490,7 +492,7 @@ 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;