iommu/amd-vi: do not error if device referenced in IVMD is not behind any IOMMU

IVMD table contains restrictions about memory which must be mandatory assigned
to devices (and which permissions it should use), or memory that should be
never accessible to devices.

Some hardware however contains ranges in IVMD that reference devices outside of
the IVHD tables (in other words, devices not behind any IOMMU).  Such mismatch
will cause Xen to fail in register_range_for_device(), ultimately leading to
the IOMMU being disabled, and Xen crashing as x2APIC support might be already
enabled and relying on the IOMMU functionality.

Relax IVMD parsing: allow IVMD blocks to reference devices not assigned to any
IOMMU.  It's impossible for Xen to fulfill the requirement in the IVMD block if
the device is not behind any IOMMU, but it's no worse than booting without
IOMMU support, and thus not parsing ACPI IVRS in the first place.

Reported-by: Willi Junga <xenproject@ymy.be>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
master commit: 2defb54490
master date: 2024-10-15 14:23:59 +0200

xen/drivers/passthrough/amd/iommu_acpi.c

@@ -248,8 +248,9 @@ static int __init register_range_for_device(
     iommu = find_iommu_for_device(seg, bdf);
     if ( !iommu )
     {
-        AMD_IOMMU_ERROR("IVMD: no IOMMU for Dev_Id %#x\n", bdf);
-        return -ENODEV;
+        AMD_IOMMU_WARN("IVMD: no IOMMU for device %pp - ignoring constrain\n",
+                       &PCI_SBDF(seg, bdf));
+        return 0;
     }
     req = ivrs_mappings[bdf].dte_requestor_id;