x86/pv: allow reading FEATURE_CONTROL MSR

Linux PV guests will attempt to read the FEATURE_CONTROL MSR, so move
the handling done in VMX code into guest_rdmsr as it can be shared
between PV and HVM guests that way.

Note that there's a slight behavior change and attempting to read the
MSR when no features are available will result in a fault.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>

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

@@ -2980,13 +2980,7 @@ static int vmx_msr_read_intercept(unsigned int msr, uint64_t *msr_content)
     case MSR_IA32_DEBUGCTLMSR:
         __vmread(GUEST_IA32_DEBUGCTL, msr_content);
         break;
-    case MSR_IA32_FEATURE_CONTROL:
-        *msr_content = IA32_FEATURE_CONTROL_LOCK;
-        if ( vmce_has_lmce(curr) )
-            *msr_content |= IA32_FEATURE_CONTROL_LMCE_ON;
-        if ( nestedhvm_enabled(curr->domain) )
-            *msr_content |= IA32_FEATURE_CONTROL_ENABLE_VMXON_OUTSIDE_SMX;
-        break;
+
     case MSR_IA32_VMX_BASIC...MSR_IA32_VMX_VMFUNC:
         if ( !nvmx_msr_read_intercept(msr, msr_content) )
             goto gp_fault;

xen/arch/x86/msr.c

@@ -25,6 +25,7 @@
 #include <xen/sched.h>
 
 #include <asm/debugreg.h>
+#include <asm/hvm/nestedhvm.h>
 #include <asm/hvm/viridian.h>
 #include <asm/msr.h>
 #include <asm/setup.h>
@@ -197,6 +198,17 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
         /* Not offered to guests. */
         goto gp_fault;
 
+    case MSR_IA32_FEATURE_CONTROL:
+        if ( !cp->basic.vmx && !vmce_has_lmce(v) )
+            goto gp_fault;
+
+        *val = IA32_FEATURE_CONTROL_LOCK;
+        if ( vmce_has_lmce(v) )
+            *val |= IA32_FEATURE_CONTROL_LMCE_ON;
+        if ( cp->basic.vmx )
+            *val |= IA32_FEATURE_CONTROL_ENABLE_VMXON_OUTSIDE_SMX;
+        break;
+
     case MSR_IA32_PLATFORM_ID:
         if ( !(cp->x86_vendor & X86_VENDOR_INTEL) ||
              !(boot_cpu_data.x86_vendor & X86_VENDOR_INTEL) )