x86: Add support for CpuidUserDis

Because CpuIdUserDis is reported in CPUID itself, the extended leaf
containing that bit must be retrieved before calling c_early_init()

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/cpu/amd.c

@@ -277,9 +277,14 @@ static void __init noinline amd_init_levelling(void)
 	 *
 	 * CPUID faulting is an Intel feature analogous to CpuidUserDis, so
 	 * that can only be present when Xen is itself virtualized (because
-	 * it can be emulated)
+	 * it can be emulated).
+	 *
+	 * Note that probing for the Intel feature _first_ isn't a mistake,
+	 * but a means to ensure MSR_INTEL_PLATFORM_INFO is read and added
+	 * to the raw CPU policy if present.
 	 */
-	if (cpu_has_hypervisor && probe_cpuid_faulting()) {
+	if ((cpu_has_hypervisor && probe_cpuid_faulting()) ||
+	    boot_cpu_has(X86_FEATURE_CPUID_USER_DIS)) {
 		expected_levelling_cap |= LCAP_faulting;
 		levelling_caps |= LCAP_faulting;
 		return;
@@ -374,6 +379,20 @@ static void __init noinline amd_init_levelling(void)
 		ctxt_switch_masking = amd_ctxt_switch_masking;
 }
 
+void amd_set_cpuid_user_dis(bool enable)
+{
+	const uint64_t bit = K8_HWCR_CPUID_USER_DIS;
+	uint64_t val;
+
+	rdmsrl(MSR_K8_HWCR, val);
+
+	if (!!(val & bit) == enable)
+		return;
+
+	val ^= bit;
+	wrmsrl(MSR_K8_HWCR, val);
+}
+
 /*
  * Check for the presence of an AMD erratum. Arguments are defined in amd.h 
  * for each known erratum. Return 1 if erratum is found.

xen/arch/x86/cpu/common.c

@@ -4,6 +4,7 @@
 #include <xen/param.h>
 #include <xen/smp.h>
 
+#include <asm/amd.h>
 #include <asm/cpu-policy.h>
 #include <asm/current.h>
 #include <asm/debugreg.h>
@@ -166,8 +167,10 @@ static void set_cpuid_faulting(bool enable)
 void ctxt_switch_levelling(const struct vcpu *next)
 {
 	const struct domain *nextd = next ? next->domain : NULL;
+	bool enable_cpuid_faulting;
 
-	if (cpu_has_cpuid_faulting) {
+	if (cpu_has_cpuid_faulting ||
+	    boot_cpu_has(X86_FEATURE_CPUID_USER_DIS)) {
 		/*
 		 * No need to alter the faulting setting if we are switching
 		 * to idle; it won't affect any code running in idle context.
@@ -188,12 +191,18 @@ void ctxt_switch_levelling(const struct vcpu *next)
 		 * an interim escape hatch in the form of
 		 * `dom0=no-cpuid-faulting` to restore the older behaviour.
 		 */
-		set_cpuid_faulting(nextd && (opt_dom0_cpuid_faulting ||
-					     !is_control_domain(nextd) ||
-					     !is_pv_domain(nextd)) &&
-				   (is_pv_domain(nextd) ||
-				    next->arch.msrs->
-				    misc_features_enables.cpuid_faulting));
+		enable_cpuid_faulting = nextd && (opt_dom0_cpuid_faulting ||
+		                                  !is_control_domain(nextd) ||
+		                                  !is_pv_domain(nextd)) &&
+		                        (is_pv_domain(nextd) ||
+		                         next->arch.msrs->
+		                         misc_features_enables.cpuid_faulting);
+
+		if (cpu_has_cpuid_faulting)
+			set_cpuid_faulting(enable_cpuid_faulting);
+		else
+			amd_set_cpuid_user_dis(enable_cpuid_faulting);
+
 		return;
 	}
 
@@ -402,6 +411,17 @@ static void generic_identify(struct cpuinfo_x86 *c)
 	c->apicid = phys_pkg_id((ebx >> 24) & 0xFF, 0);
 	c->phys_proc_id = c->apicid;
 
+	eax = cpuid_eax(0x80000000);
+	if ((eax >> 16) == 0x8000)
+		c->extended_cpuid_level = eax;
+
+	/*
+	 * These AMD-defined flags are out of place, but we need
+	 * them early for the CPUID faulting probe code
+	 */
+	if (c->extended_cpuid_level >= 0x80000021)
+		c->x86_capability[FEATURESET_e21a] = cpuid_eax(0x80000021);
+
 	if (this_cpu->c_early_init)
 		this_cpu->c_early_init(c);
 
@@ -418,10 +438,6 @@ static void generic_identify(struct cpuinfo_x86 *c)
 	     (cpuid_ecx(CPUID_PM_LEAF) & CPUID6_ECX_APERFMPERF_CAPABILITY) )
 		__set_bit(X86_FEATURE_APERFMPERF, c->x86_capability);
 
-	eax = cpuid_eax(0x80000000);
-	if ((eax >> 16) == 0x8000)
-		c->extended_cpuid_level = eax;
-
 	/* AMD-defined flags: level 0x80000001 */
 	if (c->extended_cpuid_level >= 0x80000001)
 		cpuid(0x80000001, &tmp, &tmp,

xen/arch/x86/include/asm/amd.h

@@ -155,5 +155,6 @@ extern bool amd_legacy_ssbd;
 extern bool amd_virt_spec_ctrl;
 bool amd_setup_legacy_ssbd(void);
 void amd_set_legacy_ssbd(bool enable);
+void amd_set_cpuid_user_dis(bool enable);
 
 #endif /* __AMD_H__ */