x86: don't allow Dom0 access to the HT address range

In particular, MMIO assignments should not be done using this area.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/domain_build.c
+++ b/xen/arch/x86/domain_build.c
@@ -1126,6 +1126,10 @@ int __init construct_dom0(
     rc |= iomem_deny_access(dom0, paddr_to_pfn(MSI_ADDR_BASE_LO),
                             paddr_to_pfn(MSI_ADDR_BASE_LO +
                                          MSI_ADDR_DEST_ID_MASK));
+    /* HyperTransport range. */
+    if ( boot_cpu_data.x86_vendor == X86_VENDOR_AMD )
+        rc |= iomem_deny_access(dom0, paddr_to_pfn(0xfdULL << 32),
+                                paddr_to_pfn((1ULL << 40) - 1));
 
     /* Remove access to E820_UNUSABLE I/O regions above 1MB. */
     for ( i = 0; i < e820.nr_map; i++ )