[PATCH 2/8] x86/svm: silently drop writes to SYSCFG and related MSRs

[Roger Pau Monne]

The SYSCFG, TOP_MEM1 and TOP_MEM2 MSRs are currently exposed to guests
and writes are silently discarded. Make this explicit in the SVM code
now, and just return 0 when attempting to read any of the MSRs, while
continuing to silently drop writes.

Signed-off-by: Roger Pau Monné <roger....@citrix.com>
---
 xen/arch/x86/hvm/svm/svm.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index ca3bbfcbb3..671cdcb724 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -1917,6 +1917,13 @@ static int svm_msr_read_intercept(unsigned int msr, 
uint64_t *msr_content)
             goto gpf;
         break;
 
+    case MSR_K8_TOP_MEM1:
+    case MSR_K8_TOP_MEM2:
+    case MSR_K8_SYSCFG:
+        /* Return all 0s. */
+        *msr_content = 0;
+        break;
+
     case MSR_K8_VM_CR:
         *msr_content = 0;
         break;
@@ -2094,6 +2101,12 @@ static int svm_msr_write_intercept(unsigned int msr, 
uint64_t msr_content)
             goto gpf;
         break;
 
+    case MSR_K8_TOP_MEM1:
+    case MSR_K8_TOP_MEM2:
+    case MSR_K8_SYSCFG:
+        /* Drop writes. */
+        break;
+
     case MSR_K8_VM_CR:
         /* ignore write. handle all bits as read-only. */
         break;
-- 
2.28.0