[Xen-devel] [PATCH v10 10/11] xen: add new Xen cpuid node for max address width info

[Juergen Gross <jgross@xxxxxxxx>]

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 <jgross@xxxxxxxx>
---
V10:
- correct comment in cpuid.h (Jan Beulich)

V9:
- make leaf pv-only (Jan Beulich)
- use hex value for mask (Jan Beulich)
- guest address width -> machine address width (Jan Beulich)
---
 xen/arch/x86/traps.c                |  7 +++++++
 xen/include/public/arch-x86/cpuid.h | 11 ++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index d8feef2942..2b464d02ef 100644
--- 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->a = generic_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
index d709340f18..2bc11bf6ef 100644
--- a/xen/include/public/arch-x86/cpuid.h
+++ b/xen/include/public/arch-x86/cpuid.h
@@ -85,6 +85,15 @@
 #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: 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__ */
-- 
2.12.3


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