[xen master] VT-d: check bus_to_context_maddr()'s return value

[patchbot@xxxxxxx]

commit ef5b718cf81a2448118b86b86777f9430739445d
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Oct 13 16:50:01 2025 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Oct 13 16:50:01 2025 +0200

    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@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/drivers/passthrough/vtd/iommu.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/xen/drivers/passthrough/vtd/iommu.c 
b/xen/drivers/passthrough/vtd/iommu.c
index b4105163cc..90f36ac22b 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1499,6 +1499,11 @@ 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;
@@ -1853,6 +1858,12 @@ 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];
 
--
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