exec: introduce address_space_get_iotlb_entry()

This patch introduces a helper to query the iotlb entry for a
possible iova. This will be used by later device IOTLB API to enable
the capability for a dataplane (e.g vhost) to query the IOTLB.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Cc: Richard Henderson <rth@twiddle.net>
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

exec.c

@@ -448,6 +448,39 @@ address_space_translate_internal(AddressSpaceDispatch *d, hwaddr addr, hwaddr *x
     return section;
 }
 
+/* Called from RCU critical section */
+IOMMUTLBEntry address_space_get_iotlb_entry(AddressSpace *as, hwaddr addr,
+                                            bool is_write)
+{
+    IOMMUTLBEntry iotlb = {0};
+    MemoryRegionSection *section;
+    MemoryRegion *mr;
+
+    for (;;) {
+        AddressSpaceDispatch *d = atomic_rcu_read(&as->dispatch);
+        section = address_space_lookup_region(d, addr, false);
+        addr = addr - section->offset_within_address_space
+               + section->offset_within_region;
+        mr = section->mr;
+
+        if (!mr->iommu_ops) {
+            break;
+        }
+
+        iotlb = mr->iommu_ops->translate(mr, addr, is_write);
+        if (!(iotlb.perm & (1 << is_write))) {
+            iotlb.target_as = NULL;
+            break;
+        }
+
+        addr = ((iotlb.translated_addr & ~iotlb.addr_mask)
+                | (addr & iotlb.addr_mask));
+        as = iotlb.target_as;
+    }
+
+    return iotlb;
+}
+
 /* Called from RCU critical section */
 MemoryRegion *address_space_translate(AddressSpace *as, hwaddr addr,
                                       hwaddr *xlat, hwaddr *plen,

include/exec/memory.h

@@ -1537,6 +1537,11 @@ void stl_le_phys_cached(MemoryRegionCache *cache, hwaddr addr, uint32_t val);
 void stl_be_phys_cached(MemoryRegionCache *cache, hwaddr addr, uint32_t val);
 void stq_le_phys_cached(MemoryRegionCache *cache, hwaddr addr, uint64_t val);
 void stq_be_phys_cached(MemoryRegionCache *cache, hwaddr addr, uint64_t val);
+/* address_space_get_iotlb_entry: translate an address into an IOTLB
+ * entry. Should be called from an RCU critical section.
+ */
+IOMMUTLBEntry address_space_get_iotlb_entry(AddressSpace *as, hwaddr addr,
+                                            bool is_write);
 
 /* address_space_translate: translate an address range into an address space
  * into a MemoryRegion and an address range into that section.  Should be