[Xen-devel] [PATCH RFC V4 3/5] 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, ...).

Changes since V2:
 - Split a log line differently to keep it grepable.
 - Interception for relevant MSRs will be disabled only if
   mem_access is not enabled.
 - Since they end up being disabled early on (when mem_access
   is not enabled yet), re-enable interception when mem_access
   becomes active.

Changes since V3:
 - Removed log line stating that MSR interception cannot be disabled.
 - Removed superfluous #include <asm/hvm/vmx/vmcs.h>.
 - Moved VMX-specific code to vmx.c (as a new hvm_funcs member).

Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmcs.c   |   20 ++++++++++++++++++++
 xen/arch/x86/hvm/vmx/vmx.c    |   17 +++++++++++++++++
 xen/arch/x86/mm/mem_event.c   |    3 +++
 xen/include/asm-x86/hvm/hvm.h |    2 ++
 4 files changed, 42 insertions(+)

diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 8ffc562..2703c58 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -39,6 +39,7 @@
 #include <xen/keyhandler.h>
 #include <asm/shadow.h>
 #include <asm/tboot.h>
+#include <asm/mem_event.h>
 
 static bool_t __read_mostly opt_vpid_enabled = 1;
 boolean_param("vpid", opt_vpid_enabled);
@@ -695,11 +696,30 @@ static void vmx_set_host_env(struct vcpu *v)
 void vmx_disable_intercept_for_msr(struct vcpu *v, u32 msr, int type)
 {
     unsigned long *msr_bitmap = v->arch.hvm_vmx.msr_bitmap;
+    struct domain *d = v->domain;
 
     /* VMX MSR bitmap supported? */
     if ( msr_bitmap == NULL )
         return;
 
+    if ( mem_event_check_ring(&d->mem_event->access) )
+    {
+        /* 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:
+            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.
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 2caa04a..dfb0c95 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1682,6 +1682,22 @@ void vmx_hypervisor_cpuid_leaf(uint32_t sub_idx,
         *eax |= XEN_HVM_CPUID_X2APIC_VIRT;
 }
 
+static void vmx_enable_intro_msr_interception(struct domain *d)
+{
+    struct vcpu *v;
+
+    /* Enable interception for MSRs needed for memory introspection. */
+    for_each_vcpu ( d, v )
+    {
+        vmx_enable_intercept_for_msr(v, MSR_IA32_SYSENTER_EIP, MSR_TYPE_W);
+        vmx_enable_intercept_for_msr(v, MSR_IA32_SYSENTER_ESP, MSR_TYPE_W);
+        vmx_enable_intercept_for_msr(v, MSR_IA32_SYSENTER_CS, MSR_TYPE_W);
+        vmx_enable_intercept_for_msr(v, MSR_IA32_MC0_CTL, MSR_TYPE_W);
+        vmx_enable_intercept_for_msr(v, MSR_STAR, MSR_TYPE_W);
+        vmx_enable_intercept_for_msr(v, MSR_LSTAR, MSR_TYPE_W);
+    }
+}
+
 static struct hvm_function_table __initdata vmx_function_table = {
     .name                 = "VMX",
     .cpu_up_prepare       = vmx_cpu_up_prepare,
@@ -1740,6 +1756,7 @@ static struct hvm_function_table __initdata 
vmx_function_table = {
     .handle_eoi           = vmx_handle_eoi,
     .nhvm_hap_walk_L1_p2m = nvmx_hap_walk_L1_p2m,
     .hypervisor_cpuid_leaf = vmx_hypervisor_cpuid_leaf,
+    .enable_intro_msr_interception = vmx_enable_intro_msr_interception,
 };
 
 const struct hvm_function_table * __init start_vmx(void)
diff --git a/xen/arch/x86/mm/mem_event.c b/xen/arch/x86/mm/mem_event.c
index ba7e71e..d5959d9 100644
--- a/xen/arch/x86/mm/mem_event.c
+++ b/xen/arch/x86/mm/mem_event.c
@@ -600,6 +600,9 @@ int mem_event_domctl(struct domain *d, 
xen_domctl_mem_event_op_t *mec,
             rc = mem_event_enable(d, mec, med, _VPF_mem_access, 
                                     HVM_PARAM_ACCESS_RING_PFN,
                                     mem_access_notification);
+
+            if ( rc == 0 && hvm_funcs.enable_intro_msr_interception )
+                hvm_funcs.enable_intro_msr_interception(d);
         }
         break;
 
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index 0ebd478..2a87e9b 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -205,6 +205,8 @@ struct hvm_function_table {
     void (*hypervisor_cpuid_leaf)(uint32_t sub_idx,
                                   uint32_t *eax, uint32_t *ebx,
                                   uint32_t *ecx, uint32_t *edx);
+
+    void (*enable_intro_msr_interception)(struct domain *d);
 };
 
 extern struct hvm_function_table hvm_funcs;
-- 
1.7.9.5


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