[PATCH RFC V11 2/5] xen: Optimize introspection access to guest state

[Razvan Cojocaru <rcojocaru@bitdefender.com>]

Speed optimization for introspection purposes: a handful of registers
are sent along with each mem_event. This requires enlargement of the
mem_event_request / mem_event_response stuctures, and additional code
to fill in relevant values. Since the EPT event processing code needs
more data than CR3 or MSR event processors, hvm_mem_event_fill_regs()
fills in less data than p2m_mem_event_fill_regs(), in order to avoid
overhead. Struct hvm_hw_cpu has been considered instead of the custom
struct mem_event_regs_st, but its size would cause quick filling up
of the mem_event ring buffer.

Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

---
Changes since V5:
 - Const-correctness.

Changes since V4:
 - Renamed "x86_mem_event_regs" to "mem_event_regs_x86" and
   removed a typedef.

Changes since V3:
 - Changed the name of VCPU variables referring to the current
   VCPU to "curr".
 - Renamed "mem_event_regs" to "x86_mem_event_regs" to make it
   explicit.

Changes since V2:
 - Removed inline function compiler suggestions.
 - Removed superfluous memset(&ctxt, 0, sizeof(struct hvm_hw_cpu)).
 - Padded struct mem_event_regs_st.
 - Renamed mem_event_regs_t to mem_event_regs.
 - Readability changes.

Changes since V1:
 - Replaced guest_x86_mode with cs_arbytes in the mem_event_regs_st
   structure.
 - Removed superfluous preprocessor check for __x86_64__ in
   p2m_mem_event_fill_regs().
---
 tools/libxc/xc_mem_access.c        |   10 +++++++++-
 tools/libxc/xc_mem_event.c         |    7 +++++--
 tools/libxc/xc_private.h           |    2 +-
 tools/libxc/xenctrl.h              |    2 ++
 xen/arch/x86/hvm/vmx/vmcs.c        |   25 +++++++++++++++++++++++++
 xen/arch/x86/hvm/vmx/vmx.c         |   13 +++++++++++++
 xen/arch/x86/mm/mem_event.c        |   11 +++++++++++
 xen/include/asm-x86/hvm/domain.h   |    1 +
 xen/include/asm-x86/hvm/hvm.h      |    2 ++
 xen/include/asm-x86/hvm/vmx/vmcs.h |    7 +++++++
 xen/include/public/domctl.h        |    7 ++++---
 11 files changed, 80 insertions(+), 7 deletions(-)

diff --git a/tools/libxc/xc_mem_access.c b/tools/libxc/xc_mem_access.c
index 461f0e9..55d0e9f 100644
--- a/tools/libxc/xc_mem_access.c
+++ b/tools/libxc/xc_mem_access.c
@@ -26,7 +26,15 @@
 
 void *xc_mem_access_enable(xc_interface *xch, domid_t domain_id, uint32_t *port)
 {
-    return xc_mem_event_enable(xch, domain_id, HVM_PARAM_ACCESS_RING_PFN, port);
+    return xc_mem_event_enable(xch, domain_id, HVM_PARAM_ACCESS_RING_PFN,
+                               port, 0);
+}
+
+void *xc_mem_access_enable_introspection(xc_interface *xch, domid_t domain_id,
+                                         uint32_t *port)
+{
+    return xc_mem_event_enable(xch, domain_id, HVM_PARAM_ACCESS_RING_PFN,
+                               port, 1);
 }
 
 int xc_mem_access_disable(xc_interface *xch, domid_t domain_id)
diff --git a/tools/libxc/xc_mem_event.c b/tools/libxc/xc_mem_event.c
index faf1cc6..8c0be4e 100644
--- a/tools/libxc/xc_mem_event.c
+++ b/tools/libxc/xc_mem_event.c
@@ -57,7 +57,7 @@ int xc_mem_event_memop(xc_interface *xch, domid_t domain_id,
 }
 
 void *xc_mem_event_enable(xc_interface *xch, domid_t domain_id, int param,
-                          uint32_t *port)
+                          uint32_t *port, int enable_introspection)
 {
     void *ring_page = NULL;
     uint64_t pfn;
@@ -120,7 +120,10 @@ void *xc_mem_event_enable(xc_interface *xch, domid_t domain_id, int param,
         break;
 
     case HVM_PARAM_ACCESS_RING_PFN:
-        op = XEN_DOMCTL_MEM_EVENT_OP_ACCESS_ENABLE;
+        if ( enable_introspection )
+            op = XEN_DOMCTL_MEM_EVENT_OP_ACCESS_ENABLE_INTROSPECTION;
+        else
+            op = XEN_DOMCTL_MEM_EVENT_OP_ACCESS_ENABLE;
         mode = XEN_DOMCTL_MEM_EVENT_OP_ACCESS;
         break;
 
diff --git a/tools/libxc/xc_private.h b/tools/libxc/xc_private.h
index c50a7c9..94df688 100644
--- a/tools/libxc/xc_private.h
+++ b/tools/libxc/xc_private.h
@@ -381,6 +381,6 @@ int xc_mem_event_memop(xc_interface *xch, domid_t domain_id,
  * param can be HVM_PARAM_PAGING/ACCESS/SHARING_RING_PFN
  */
 void *xc_mem_event_enable(xc_interface *xch, domid_t domain_id, int param,
-                          uint32_t *port);
+                          uint32_t *port, int enable_introspection);
 
 #endif /* __XC_PRIVATE_H__ */
diff --git a/tools/libxc/xenctrl.h b/tools/libxc/xenctrl.h
index 1c5d0db..28b5562 100644
--- a/tools/libxc/xenctrl.h
+++ b/tools/libxc/xenctrl.h
@@ -2263,6 +2263,8 @@ int xc_mem_paging_load(xc_interface *xch, domid_t domain_id,
  * Caller has to unmap this page when done.
  */
 void *xc_mem_access_enable(xc_interface *xch, domid_t domain_id, uint32_t *port);
+void *xc_mem_access_enable_introspection(xc_interface *xch, domid_t domain_id,
+                                         uint32_t *port);
 int xc_mem_access_disable(xc_interface *xch, domid_t domain_id);
 int xc_mem_access_resume(xc_interface *xch, domid_t domain_id);
 
diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 4a4f4e1..fc1f882 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);
@@ -71,6 +72,18 @@ u32 vmx_vmexit_control __read_mostly;
 u32 vmx_vmentry_control __read_mostly;
 u64 vmx_ept_vpid_cap __read_mostly;
 
+const u32 vmx_introspection_force_enabled_msrs[] = {
+    MSR_IA32_SYSENTER_EIP,
+    MSR_IA32_SYSENTER_ESP,
+    MSR_IA32_SYSENTER_CS,
+    MSR_IA32_MC0_CTL,
+    MSR_STAR,
+    MSR_LSTAR
+};
+
+const unsigned int vmx_introspection_force_enabled_msrs_size =
+    ARRAY_SIZE(vmx_introspection_force_enabled_msrs);
+
 static DEFINE_PER_CPU_READ_MOSTLY(struct vmcs_struct *, vmxon_region);
 static DEFINE_PER_CPU(struct vmcs_struct *, current_vmcs);
 static DEFINE_PER_CPU(struct list_head, active_vmcs_list);
@@ -695,11 +708,23 @@ 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 ( unlikely(d->arch.hvm_domain.introspection_enabled) &&
+         mem_event_check_ring(&d->mem_event->access) )
+    {
+        unsigned int i;
+
+        /* Filter out MSR-s needed for memory introspection */
+        for ( i = 0; i < vmx_introspection_force_enabled_msrs_size; i++ )
+            if ( msr == vmx_introspection_force_enabled_msrs[i] )
+                return;
+    }
+
     /*
      * 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 26b1ad5..b08664e 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1683,6 +1683,18 @@ void vmx_hypervisor_cpuid_leaf(uint32_t sub_idx,
         *eax |= XEN_HVM_CPUID_X2APIC_VIRT;
 }
 
+static void vmx_enable_msr_exit_interception(struct domain *d)
+{
+    struct vcpu *v;
+    unsigned int i;
+
+    /* Enable interception for MSRs needed for memory introspection. */
+    for_each_vcpu ( d, v )
+        for ( i = 0; i < vmx_introspection_force_enabled_msrs_size; i++ )
+            vmx_enable_intercept_for_msr(v, vmx_introspection_force_enabled_msrs[i],
+                                         MSR_TYPE_W);
+}
+
 static struct hvm_function_table __initdata vmx_function_table = {
     .name                 = "VMX",
     .cpu_up_prepare       = vmx_cpu_up_prepare,
@@ -1741,6 +1753,7 @@ 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_msr_exit_interception = vmx_enable_msr_exit_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..fdd5ff6 100644
--- a/xen/arch/x86/mm/mem_event.c
+++ b/xen/arch/x86/mm/mem_event.c
@@ -587,6 +587,7 @@ int mem_event_domctl(struct domain *d, xen_domctl_mem_event_op_t *mec,
         switch( mec->op )
         {
         case XEN_DOMCTL_MEM_EVENT_OP_ACCESS_ENABLE:
+        case XEN_DOMCTL_MEM_EVENT_OP_ACCESS_ENABLE_INTROSPECTION:
         {
             rc = -ENODEV;
             /* Only HAP is supported */
@@ -600,13 +601,23 @@ 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 ( mec->op != XEN_DOMCTL_MEM_EVENT_OP_ACCESS_ENABLE &&
+                 rc == 0 && hvm_funcs.enable_msr_exit_interception )
+            {
+                d->arch.hvm_domain.introspection_enabled = 1;
+                hvm_funcs.enable_msr_exit_interception(d);
+            }
         }
         break;
 
         case XEN_DOMCTL_MEM_EVENT_OP_ACCESS_DISABLE:
         {
             if ( med->ring_page )
+            {
                 rc = mem_event_disable(d, med);
+                d->arch.hvm_domain.introspection_enabled = 0;
+            }
         }
         break;
 
diff --git a/xen/include/asm-x86/hvm/domain.h b/xen/include/asm-x86/hvm/domain.h
index 291a2e0..30d4aa3 100644
--- a/xen/include/asm-x86/hvm/domain.h
+++ b/xen/include/asm-x86/hvm/domain.h
@@ -134,6 +134,7 @@ struct hvm_domain {
     bool_t                 mem_sharing_enabled;
     bool_t                 qemu_mapcache_invalidate;
     bool_t                 is_s3_suspended;
+    bool_t                 introspection_enabled;
 
     /*
      * TSC value that VCPUs use to calculate their tsc_offset value.
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index 1123857..121d053 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_msr_exit_interception)(struct domain *d);
 };
 
 extern struct hvm_function_table hvm_funcs;
diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h b/xen/include/asm-x86/hvm/vmx/vmcs.h
index 215d93c..6a99dca 100644
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -471,6 +471,13 @@ enum vmcs_field {
     HOST_RIP                        = 0x00006c16,
 };
 
+/*
+ * A set of MSR-s that need to be enabled for memory introspection
+ * to work.
+ */
+extern const u32 vmx_introspection_force_enabled_msrs[];
+extern const unsigned int vmx_introspection_force_enabled_msrs_size;
+
 #define VMCS_VPID_WIDTH 16
 
 #define MSR_TYPE_R 1
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index 5b11bbf..a3431ec 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -772,10 +772,11 @@ struct xen_domctl_gdbsx_domstatus {
  * ENODEV - host lacks HAP support (EPT/NPT) or HAP is disabled in guest
  * EBUSY  - guest has or had access enabled, ring buffer still active
  */
-#define XEN_DOMCTL_MEM_EVENT_OP_ACCESS            2
+#define XEN_DOMCTL_MEM_EVENT_OP_ACCESS                        2
 
-#define XEN_DOMCTL_MEM_EVENT_OP_ACCESS_ENABLE     0
-#define XEN_DOMCTL_MEM_EVENT_OP_ACCESS_DISABLE    1
+#define XEN_DOMCTL_MEM_EVENT_OP_ACCESS_ENABLE                 0
+#define XEN_DOMCTL_MEM_EVENT_OP_ACCESS_DISABLE                1
+#define XEN_DOMCTL_MEM_EVENT_OP_ACCESS_ENABLE_INTROSPECTION   2
 
 /*
  * Sharing ENOMEM helper.
-- 
1.7.9.5