[PATCH v5 2/2] intel_iommu: Take locks when looking for and creating address spaces

[CLEMENT MATHIEU--DRIF]

vtd_find_add_as can be called by multiple threads which leads to a race
condition. Taking the IOMMU lock ensures we avoid such a race.
Moreover we also need to take the bql to avoid an assert to fail in
memory_region_add_subregion_overlap when actually allocating a new
address space.

Signed-off-by: Clement Mathieu--Drif <clement.mathieu--d...@eviden.com>
---
 hw/i386/intel_iommu.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index dad1d9f300..144e25622a 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -4205,9 +4205,30 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, 
PCIBus *bus,
     VTDAddressSpace *vtd_dev_as;
     char name[128];
 
+    vtd_iommu_lock(s);
     vtd_dev_as = g_hash_table_lookup(s->vtd_address_spaces, &key);
+    vtd_iommu_unlock(s);
+
     if (!vtd_dev_as) {
-        struct vtd_as_key *new_key = g_malloc(sizeof(*new_key));
+        struct vtd_as_key *new_key;
+        /* Slow path */
+
+        /*
+        * memory_region_add_subregion_overlap requires the bql,
+        * make sure we own it.
+        */
+        BQL_LOCK_GUARD();
+        vtd_iommu_lock(s);
+
+        /* Check again as we released the lock for a moment */
+        vtd_dev_as = g_hash_table_lookup(s->vtd_address_spaces, &key);
+        if (vtd_dev_as) {
+            vtd_iommu_unlock(s);
+            return vtd_dev_as;
+        }
+
+        /* Still nothing, allocate a new address space */
+        new_key = g_malloc(sizeof(*new_key));
 
         new_key->bus = bus;
         new_key->devfn = devfn;
@@ -4298,6 +4319,8 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, 
PCIBus *bus,
         vtd_switch_address_space(vtd_dev_as);
 
         g_hash_table_insert(s->vtd_address_spaces, new_key, vtd_dev_as);
+    
+        vtd_iommu_unlock(s);
     }
     return vtd_dev_as;
 }
-- 
2.49.0