File 68ed1199-VT-d-bus_to_context_maddr-retval.patch of Package xen.41885

# Commit ef5b718cf81a2448118b86b86777f9430739445d
# Date 2025-10-13 16:50:01 +0200
# Author Jan Beulich <jbeulich@suse.com>
# Committer Jan Beulich <jbeulich@suse.com>
VT-d: check bus_to_context_maddr()'s return value

The function returning zero is an error indication; we shouldn't try to
map MFN 0 and then treat that page as a context table.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1496,6 +1496,11 @@ int domain_context_mapping_one(
     ASSERT(pcidevs_locked());
     spin_lock(&iommu->lock);
     maddr = bus_to_context_maddr(iommu, bus);
+    if ( !maddr )
+    {
+        spin_unlock(&iommu->lock);
+        return -ENOMEM;
+    }
     context_entries = (struct context_entry *)map_vtd_domain_page(maddr);
     context = &context_entries[devfn];
     old = (lctxt = *context).full;
@@ -1888,6 +1893,12 @@ int domain_context_unmap_one(
     spin_lock(&iommu->lock);
 
     maddr = bus_to_context_maddr(iommu, bus);
+    if ( !maddr )
+    {
+        ASSERT_UNREACHABLE();
+        spin_unlock(&iommu->lock);
+        return 0;
+    }
     context_entries = (struct context_entry *)map_vtd_domain_page(maddr);
     context = &context_entries[devfn];