VMX: don't blindly enable descriptor table exiting control

This is an optional feature and hence we should check for it before
use.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>

xen/arch/x86/hvm/vmx/vmcs.c

@@ -226,6 +226,7 @@ static int vmx_init_vmcs_config(void)
         opt = (SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
                SECONDARY_EXEC_WBINVD_EXITING |
                SECONDARY_EXEC_ENABLE_EPT |
+               SECONDARY_EXEC_DESCRIPTOR_TABLE_EXITING |
                SECONDARY_EXEC_ENABLE_RDTSCP |
                SECONDARY_EXEC_PAUSE_LOOP_EXITING |
                SECONDARY_EXEC_ENABLE_INVPCID |
@@ -1020,6 +1021,13 @@ static int construct_vmcs(struct vcpu *v)
 
     v->arch.hvm_vmx.secondary_exec_control = vmx_secondary_exec_control;
 
+    /*
+     * Disable descriptor table exiting: It's controlled by the VM event
+     * monitor requesting it.
+     */
+    v->arch.hvm_vmx.secondary_exec_control &=
+        ~SECONDARY_EXEC_DESCRIPTOR_TABLE_EXITING;
+
     /* Disable VPID for now: we decide when to enable it on VMENTER. */
     v->arch.hvm_vmx.secondary_exec_control &= ~SECONDARY_EXEC_ENABLE_VPID;
 

xen/arch/x86/hvm/vmx/vmx.c

@@ -2325,7 +2325,6 @@ static struct hvm_function_table __initdata vmx_function_table = {
     .handle_cd            = vmx_handle_cd,
     .set_info_guest       = vmx_set_info_guest,
     .set_rdtsc_exiting    = vmx_set_rdtsc_exiting,
-    .set_descriptor_access_exiting = vmx_set_descriptor_access_exiting,
     .nhvm_vcpu_initialise = nvmx_vcpu_initialise,
     .nhvm_vcpu_destroy    = nvmx_vcpu_destroy,
     .nhvm_vcpu_reset      = nvmx_vcpu_reset,
@@ -2446,6 +2445,10 @@ const struct hvm_function_table * __init start_vmx(void)
         return NULL;
     }
 
+    if ( cpu_has_vmx_dt_exiting )
+        vmx_function_table.set_descriptor_access_exiting =
+            vmx_set_descriptor_access_exiting;
+
     /*
      * Do not enable EPT when (!cpu_has_vmx_pat), to prevent security hole
      * (refer to http://xenbits.xen.org/xsa/advisory-60.html).

xen/arch/x86/monitor.c

@@ -219,6 +219,9 @@ int arch_monitor_domctl_event(struct domain *d,
         if ( unlikely(old_status == requested_status) )
             return -EEXIST;
 
+        if ( !hvm_funcs.set_descriptor_access_exiting )
+            return -EOPNOTSUPP;
+
         domain_pause(d);
         ad->monitor.descriptor_access_enabled = requested_status;
 

xen/include/asm-x86/hvm/vmx/vmcs.h

@@ -274,6 +274,8 @@ extern u64 vmx_ept_vpid_cap;
     (vmx_cpu_based_exec_control & CPU_BASED_ACTIVATE_SECONDARY_CONTROLS)
 #define cpu_has_vmx_ept \
     (vmx_secondary_exec_control & SECONDARY_EXEC_ENABLE_EPT)
+#define cpu_has_vmx_dt_exiting \
+    (vmx_secondary_exec_control & SECONDARY_EXEC_DESCRIPTOR_TABLE_EXITING)
 #define cpu_has_vmx_vpid \
     (vmx_secondary_exec_control & SECONDARY_EXEC_ENABLE_VPID)
 #define cpu_has_monitor_trap_flag \

xen/include/asm-x86/monitor.h

@@ -77,13 +77,15 @@ static inline uint32_t arch_monitor_get_capabilities(struct domain *d)
                    (1U << XEN_DOMCTL_MONITOR_EVENT_GUEST_REQUEST) |
                    (1U << XEN_DOMCTL_MONITOR_EVENT_DEBUG_EXCEPTION) |
                    (1U << XEN_DOMCTL_MONITOR_EVENT_CPUID) |
-                   (1U << XEN_DOMCTL_MONITOR_EVENT_INTERRUPT) |
-                   (1U << XEN_DOMCTL_MONITOR_EVENT_DESC_ACCESS);
+                   (1U << XEN_DOMCTL_MONITOR_EVENT_INTERRUPT);
 
     /* Since we know this is on VMX, we can just call the hvm func */
     if ( hvm_is_singlestep_supported() )
         capabilities |= (1U << XEN_DOMCTL_MONITOR_EVENT_SINGLESTEP);
 
+    if ( hvm_funcs.set_descriptor_access_exiting )
+        capabilities |= (1U << XEN_DOMCTL_MONITOR_EVENT_DESC_ACCESS);
+
     return capabilities;
 }