[Xen-devel] [PATCH RFC V2 3/6] xen: Force-enable relevant MSR events; optimize the number of sent MSR events

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

Vmx_disable_intercept_for_msr() will now refuse to disable interception of
MSRs needed for memory introspection. It is not possible to gate this on
mem_access being active for the domain, since by the time mem_access does
become active the interception for the interesting MSRs has already been
disabled (vmx_disable_intercept_for_msr() runs very early on).

Changes since V1:
 - Replaced printk() with gdprintk(XENLOG_DEBUG, ...).

Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmcs.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 8ffc562..35fcfcc 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -700,6 +700,24 @@ void vmx_disable_intercept_for_msr(struct vcpu *v, u32 
msr, int type)
     if ( msr_bitmap == NULL )
         return;
 
+    /* Filter out MSR-s needed for memory introspection */
+    switch ( msr )
+    {
+    case MSR_IA32_SYSENTER_EIP:
+    case MSR_IA32_SYSENTER_ESP:
+    case MSR_IA32_SYSENTER_CS:
+    case MSR_IA32_MC0_CTL:
+    case MSR_STAR:
+    case MSR_LSTAR:
+
+        gdprintk(XENLOG_DEBUG, "MSR 0x%08x needed for "
+            "memory introspection, still intercepted\n", msr);
+        return;
+
+    default:
+        break;
+    }
+
     /*
      * See Intel PRM Vol. 3, 20.6.9 (MSR-Bitmap Address). Early manuals
      * have the write-low and read-high bitmap offsets the wrong way round.
-- 
1.7.9.5


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