x86/hvm: Conditionally leave CPUID Faulting active in HVM context

If the hardware supports faulting, and the guest has chosen to use it, leave
faulting active in HVM context.

It is more efficient to have hardware convert CPUID to a #GP fault (which we
don't intercept), than to take a VMExit and have Xen re-inject a #GP fault.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>

diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c
index 2e11662f7a72ff86530b8f1cdacd48307c26c202..d0e380c3c612347dfc54b1105bee4f0a83073fc5 100644 (file)
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -175,8 +175,9 @@ static void intel_ctxt_switch_levelling(const struct vcpu *next)
                 * generating the maximum full cpuid policy into Xen, at which
                 * this problem will disappear.
                 */
-               set_cpuid_faulting(nextd && is_pv_domain(nextd) &&
-                                  !is_control_domain(nextd));
+               set_cpuid_faulting(nextd && !is_control_domain(nextd) &&
+                                  (is_pv_domain(nextd) ||
+                                   next->arch.cpuid_faulting));
                return;
        }
 

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index a5e5ffdcac793cebf933d642a752b2fc743733f1..dcb308cdf7c6a714966f579fa3ead89593cb58c3 100644 (file)
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2866,11 +2866,19 @@ static int vmx_msr_write_intercept(unsigned int msr, uint64_t msr_content)
         break;
 
     case MSR_INTEL_MISC_FEATURES_ENABLES:
+    {
+        bool old_cpuid_faulting = v->arch.cpuid_faulting;
+
         if ( msr_content & ~MSR_MISC_FEATURES_CPUID_FAULTING )
             goto gp_fault;
-        v->arch.cpuid_faulting =
-            !!(msr_content & MSR_MISC_FEATURES_CPUID_FAULTING);
+
+        v->arch.cpuid_faulting = msr_content & MSR_MISC_FEATURES_CPUID_FAULTING;
+
+        if ( cpu_has_cpuid_faulting &&
+             (old_cpuid_faulting ^ v->arch.cpuid_faulting) )
+            ctxt_switch_levelling(v);
         break;
+    }
 
     default:
         if ( passive_domain_do_wrmsr(msr, msr_content) )