x86: add new Xen cpuid node for max address width info

On very large hosts a pv-guest needs to know whether it will have to handle frame numbers larger than 32 bits in order to select the appropriate grant interface version. Add a new Xen specific CPUID node to contain the maximum machine address width similar to the x86 CPUID node 0x80000008 containing the maximum physical address width. The maximum frame width needs to take memory hotplug into account. Signed-off-by: Juergen Gross <[email protected]> Reviewed-by: Jan Beulich <[email protected]>
kaustubhcs · Sep 28, 2017 · c3d74ac · c3d74ac
1 parent 0c1ffc6
commit c3d74ac
Show file tree

Hide file tree

Showing 2 changed files with 18 additions and 1 deletion.
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
@@ -930,6 +930,13 @@ void cpuid_hypervisor_leaves(const struct vcpu *v, uint32_t leaf,
         res->b = v->vcpu_id;
         break;
 
+    case 5: /* PV-specific parameters */
+        if ( is_hvm_domain(d) || subleaf != 0 )
+            break;
+
+        res->b = flsl(get_upper_mfn_bound()) + PAGE_SHIFT;
+        break;
+
     default:
         ASSERT_UNREACHABLE();
     }

diff --git a/xen/include/public/arch-x86/cpuid.h b/xen/include/public/arch-x86/cpuid.h
@@ -85,6 +85,16 @@
 #define XEN_HVM_CPUID_IOMMU_MAPPINGS   (1u << 2)
 #define XEN_HVM_CPUID_VCPU_ID_PRESENT  (1u << 3) /* vcpu id is present in EBX */
 
-#define XEN_CPUID_MAX_NUM_LEAVES 4
+/*
+ * Leaf 6 (0x40000x05)
+ * PV-specific parameters
+ * Sub-leaf 0: EAX: max available sub-leaf
+ * Sub-leaf 0: EBX: bits 0-7: max machine address width
+ */
+
+/* Max. address width in bits taking memory hotplug into account. */
+#define XEN_CPUID_MACHINE_ADDRESS_WIDTH_MASK (0xffu << 0)
+
+#define XEN_CPUID_MAX_NUM_LEAVES 5
 
 #endif /* __XEN_PUBLIC_ARCH_X86_CPUID_H__ */