[PATCH v2 2/4] x86: Introduce MSR_UNHANDLED

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

When toolstack updates MSR policy, this MSR offset (which is the last
index in the hypervisor MSR range) is used to indicate hypervisor
behavior when guest accesses an MSR which is not explicitly emulated.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
Changes in v2:
* Use 0x400002ff for MSR_UNHANDLED
* Pass ignore_msrs in msr_policy.value

 xen/arch/x86/msr.c            |  4 ++--
 xen/include/xen/lib/x86/msr.h | 17 ++++++++++++++++-
 xen/lib/x86/msr.c             |  2 ++
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index be8e36386250..433d16c80728 100644
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -295,7 +295,7 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
         }
 
         /* Fallthrough. */
-    case 0x40000200 ... 0x400002ff:
+    case 0x40000200 ... 0x400002fe:
         ret = guest_rdmsr_xen(v, msr, val);
         break;
 
@@ -514,7 +514,7 @@ int guest_wrmsr(struct vcpu *v, uint32_t msr, uint64_t val)
         }
 
         /* Fallthrough. */
-    case 0x40000200 ... 0x400002ff:
+    case 0x40000200 ... 0x400002fe:
         ret = guest_wrmsr_xen(v, msr, val);
         break;
 
diff --git a/xen/include/xen/lib/x86/msr.h b/xen/include/xen/lib/x86/msr.h
index 48ba4a59c036..fbbb3b7ba870 100644
--- a/xen/include/xen/lib/x86/msr.h
+++ b/xen/include/xen/lib/x86/msr.h
@@ -2,8 +2,21 @@
 #ifndef XEN_LIB_X86_MSR_H
 #define XEN_LIB_X86_MSR_H
 
+/*
+ * Behavior on accesses to MSRs that are not handled by emulation:
+ *  0 = return #GP, warning emitted
+ *  1 = read as 0, writes are dropped, no warning
+ *  2 = read as 0, writes are dropped, warning emitted
+ */
+#define MSR_UNHANDLED_NEVER     0
+#define MSR_UNHANDLED_SILENT    1
+#define MSR_UNHANDLED_VERBOSE   2
+
+/* MSR that is not explicitly processed by emulation */
+#define MSR_UNHANDLED           0x400002ff
+
 /* Maximum number of MSRs written when serialising msr_policy. */
-#define MSR_MAX_SERIALISED_ENTRIES 2
+#define MSR_MAX_SERIALISED_ENTRIES 3
 
 /* MSR policy object for shared per-domain MSRs */
 struct msr_policy
@@ -45,6 +58,8 @@ struct msr_policy
             bool taa_no:1;
         };
     } arch_caps;
+
+    uint8_t ignore_msrs;
 };
 
 #ifdef __XEN__
diff --git a/xen/lib/x86/msr.c b/xen/lib/x86/msr.c
index 7d71e92a380a..178203803946 100644
--- a/xen/lib/x86/msr.c
+++ b/xen/lib/x86/msr.c
@@ -40,6 +40,7 @@ int x86_msr_copy_to_buffer(const struct msr_policy *p,
 
     COPY_MSR(MSR_INTEL_PLATFORM_INFO, p->platform_info.raw);
     COPY_MSR(MSR_ARCH_CAPABILITIES,   p->arch_caps.raw);
+    COPY_MSR(MSR_UNHANDLED,           p->ignore_msrs);
 
 #undef COPY_MSR
 
@@ -101,6 +102,7 @@ int x86_msr_copy_from_buffer(struct msr_policy *p,
 
         case MSR_INTEL_PLATFORM_INFO: ASSIGN(platform_info.raw); break;
         case MSR_ARCH_CAPABILITIES:   ASSIGN(arch_caps.raw);     break;
+        case MSR_UNHANDLED:           ASSIGN(ignore_msrs);       break;
 
 #undef ASSIGN
 
-- 
1.8.3.1