x86: Common cpuid faulting support

With CPUID Faulting offered to SVM guests, move Xen's faulting code to being
common rather than Intel specific.

This is necessary for nested Xen (inc. pv-shim mode) to prevent PV guests from
finding the outer HVM Xen leaves via native cpuid.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>

xen/arch/x86/cpu/amd.c

@@ -198,11 +198,12 @@ static void __init noinline probe_masking_msrs(void)
 }
 
 /*
- * Context switch levelling state to the next domain.  A parameter of NULL is
- * used to context switch to the default host state (by the cpu bringup-code,
- * crash path, etc).
+ * Context switch CPUID masking state to the next domain.  Only called if
+ * CPUID Faulting isn't available, but masking MSRs have been detected.  A
+ * parameter of NULL is used to context switch to the default host state (by
+ * the cpu bringup-code, crash path, etc).
  */
-static void amd_ctxt_switch_levelling(const struct vcpu *next)
+static void amd_ctxt_switch_masking(const struct vcpu *next)
 {
 	struct cpuidmasks *these_masks = &this_cpu(cpuidmasks);
 	const struct domain *nextd = next ? next->domain : NULL;
@@ -263,6 +264,9 @@ static void __init noinline amd_init_levelling(void)
 {
 	const struct cpuidmask *m = NULL;
 
+	if (probe_cpuid_faulting())
+		return;
+
 	probe_masking_msrs();
 
 	if (*opt_famrev != '\0') {
@@ -352,7 +356,7 @@ static void __init noinline amd_init_levelling(void)
 	}
 
 	if (levelling_caps)
-		ctxt_switch_levelling = amd_ctxt_switch_levelling;
+		ctxt_switch_masking = amd_ctxt_switch_masking;
 }
 
 /*
@@ -518,7 +522,7 @@ static void early_init_amd(struct cpuinfo_x86 *c)
 	if (c == &boot_cpu_data)
 		amd_init_levelling();
 
-	amd_ctxt_switch_levelling(NULL);
+	ctxt_switch_levelling(NULL);
 }
 
 static void init_amd(struct cpuinfo_x86 *c)

xen/arch/x86/cpu/common.c

@@ -113,12 +113,80 @@ static const struct cpu_dev default_cpu = {
 };
 static const struct cpu_dev *this_cpu = &default_cpu;
 
-static void default_ctxt_switch_levelling(const struct vcpu *next)
+static DEFINE_PER_CPU(uint64_t, msr_misc_features);
+void (* __read_mostly ctxt_switch_masking)(const struct vcpu *next);
+
+bool __init probe_cpuid_faulting(void)
 {
-	/* Nop */
+	uint64_t val;
+
+	if (rdmsr_safe(MSR_INTEL_PLATFORM_INFO, val) ||
+	    !(val & MSR_PLATFORM_INFO_CPUID_FAULTING) ||
+	    rdmsr_safe(MSR_INTEL_MISC_FEATURES_ENABLES,
+		       this_cpu(msr_misc_features)))
+	{
+		setup_clear_cpu_cap(X86_FEATURE_CPUID_FAULTING);
+		return false;
+	}
+
+	expected_levelling_cap |= LCAP_faulting;
+	levelling_caps |=  LCAP_faulting;
+	setup_force_cpu_cap(X86_FEATURE_CPUID_FAULTING);
+
+	return true;
+}
+
+static void set_cpuid_faulting(bool enable)
+{
+	uint64_t *this_misc_features = &this_cpu(msr_misc_features);
+	uint64_t val = *this_misc_features;
+
+	if (!!(val & MSR_MISC_FEATURES_CPUID_FAULTING) == enable)
+		return;
+
+	val ^= MSR_MISC_FEATURES_CPUID_FAULTING;
+
+	wrmsrl(MSR_INTEL_MISC_FEATURES_ENABLES, val);
+	*this_misc_features = val;
+}
+
+void ctxt_switch_levelling(const struct vcpu *next)
+{
+	const struct domain *nextd = next ? next->domain : NULL;
+
+	if (cpu_has_cpuid_faulting) {
+		/*
+		 * No need to alter the faulting setting if we are switching
+		 * to idle; it won't affect any code running in idle context.
+		 */
+		if (nextd && is_idle_domain(nextd))
+			return;
+		/*
+		 * We *should* be enabling faulting for the control domain.
+		 *
+		 * Unfortunately, the domain builder (having only ever been a
+		 * PV guest) expects to be able to see host cpuid state in a
+		 * native CPUID instruction, to correctly build a CPUID policy
+		 * for HVM guests (notably the xstate leaves).
+		 *
+		 * This logic is fundimentally broken for HVM toolstack
+		 * domains, and faulting causes PV guests to behave like HVM
+		 * guests from their point of view.
+		 *
+		 * Future development plans will move responsibility for
+		 * generating the maximum full cpuid policy into Xen, at which
+		 * this problem will disappear.
+		 */
+		set_cpuid_faulting(nextd && !is_control_domain(nextd) &&
+				   (is_pv_domain(nextd) ||
+				    next->arch.msr->
+				    misc_features_enables.cpuid_faulting));
+		return;
+	}
+
+	if (ctxt_switch_masking)
+		ctxt_switch_masking(next);
 }
-void (* __read_mostly ctxt_switch_levelling)(const struct vcpu *next) =
-	default_ctxt_switch_levelling;
 
 bool_t opt_cpu_info;
 boolean_param("cpuinfo", opt_cpu_info);

xen/arch/x86/cpu/intel.c

@@ -15,41 +15,6 @@
 
 #include "cpu.h"
 
-static bool __init probe_intel_cpuid_faulting(void)
-{
-	uint64_t x;
-
-	if (rdmsr_safe(MSR_INTEL_PLATFORM_INFO, x) ||
-	    !(x & MSR_PLATFORM_INFO_CPUID_FAULTING))
-		return 0;
-
-	expected_levelling_cap |= LCAP_faulting;
-	levelling_caps |=  LCAP_faulting;
-	setup_force_cpu_cap(X86_FEATURE_CPUID_FAULTING);
-	return 1;
-}
-
-DEFINE_PER_CPU(bool, cpuid_faulting_enabled);
-
-static void set_cpuid_faulting(bool enable)
-{
-	bool *this_enabled = &this_cpu(cpuid_faulting_enabled);
-	uint32_t hi, lo;
-
-	ASSERT(cpu_has_cpuid_faulting);
-
-	if (*this_enabled == enable)
-		return;
-
-	rdmsr(MSR_INTEL_MISC_FEATURES_ENABLES, lo, hi);
-	lo &= ~MSR_MISC_FEATURES_CPUID_FAULTING;
-	if (enable)
-		lo |= MSR_MISC_FEATURES_CPUID_FAULTING;
-	wrmsr(MSR_INTEL_MISC_FEATURES_ENABLES, lo, hi);
-
-	*this_enabled = enable;
-}
-
 /*
  * Set caps in expected_levelling_cap, probe a specific masking MSR, and set
  * caps in levelling_caps if it is found, or clobber the MSR index if missing.
@@ -145,40 +110,17 @@ static void __init probe_masking_msrs(void)
 }
 
 /*
- * Context switch levelling state to the next domain.  A parameter of NULL is
- * used to context switch to the default host state (by the cpu bringup-code,
- * crash path, etc).
+ * Context switch CPUID masking state to the next domain.  Only called if
+ * CPUID Faulting isn't available, but masking MSRs have been detected.  A
+ * parameter of NULL is used to context switch to the default host state (by
+ * the cpu bringup-code, crash path, etc).
  */
-static void intel_ctxt_switch_levelling(const struct vcpu *next)
+static void intel_ctxt_switch_masking(const struct vcpu *next)
 {
 	struct cpuidmasks *these_masks = &this_cpu(cpuidmasks);
 	const struct domain *nextd = next ? next->domain : NULL;
-	const struct cpuidmasks *masks;
-
-	if (cpu_has_cpuid_faulting) {
-		/*
-		 * We *should* be enabling faulting for the control domain.
-		 *
-		 * Unfortunately, the domain builder (having only ever been a
-		 * PV guest) expects to be able to see host cpuid state in a
-		 * native CPUID instruction, to correctly build a CPUID policy
-		 * for HVM guests (notably the xstate leaves).
-		 *
-		 * This logic is fundimentally broken for HVM toolstack
-		 * domains, and faulting causes PV guests to behave like HVM
-		 * guests from their point of view.
-		 *
-		 * Future development plans will move responsibility for
-		 * generating the maximum full cpuid policy into Xen, at which
-		 * this problem will disappear.
-		 */
-		set_cpuid_faulting(nextd && !is_control_domain(nextd) &&
-				   (is_pv_domain(nextd) ||
-				    next->arch.msr->misc_features_enables.cpuid_faulting));
-		return;
-	}
-
-	masks = (nextd && is_pv_domain(nextd) && nextd->arch.pv_domain.cpuidmasks)
+	const struct cpuidmasks *masks =
+		(nextd && is_pv_domain(nextd) && nextd->arch.pv_domain.cpuidmasks)
 		? nextd->arch.pv_domain.cpuidmasks : &cpuidmask_defaults;
 
         if (msr_basic) {
@@ -223,8 +165,10 @@ static void intel_ctxt_switch_levelling(const struct vcpu *next)
  */
 static void __init noinline intel_init_levelling(void)
 {
-	if (!probe_intel_cpuid_faulting())
-		probe_masking_msrs();
+	if (probe_cpuid_faulting())
+		return;
+
+	probe_masking_msrs();
 
 	if (msr_basic) {
 		uint32_t ecx, edx, tmp;
@@ -278,7 +222,7 @@ static void __init noinline intel_init_levelling(void)
 	}
 
 	if (levelling_caps)
-		ctxt_switch_levelling = intel_ctxt_switch_levelling;
+		ctxt_switch_masking = intel_ctxt_switch_masking;
 }
 
 static void early_init_intel(struct cpuinfo_x86 *c)
@@ -316,7 +260,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 	if (c == &boot_cpu_data)
 		intel_init_levelling();
 
-	intel_ctxt_switch_levelling(NULL);
+	ctxt_switch_levelling(NULL);
 }
 
 /*

xen/include/asm-x86/cpuid.h

@@ -58,9 +58,6 @@ DECLARE_PER_CPU(struct cpuidmasks, cpuidmasks);
 /* Default masking MSR values, calculated at boot. */
 extern struct cpuidmasks cpuidmask_defaults;
 
-/* Whether or not cpuid faulting is available for the current domain. */
-DECLARE_PER_CPU(bool, cpuid_faulting_enabled);
-
 #define CPUID_GUEST_NR_BASIC      (0xdu + 1)
 #define CPUID_GUEST_NR_FEAT       (0u + 1)
 #define CPUID_GUEST_NR_CACHE      (5u + 1)

xen/include/asm-x86/processor.h

@@ -151,7 +151,9 @@ extern struct cpuinfo_x86 boot_cpu_data;
 extern struct cpuinfo_x86 cpu_data[];
 #define current_cpu_data cpu_data[smp_processor_id()]
 
-extern void (*ctxt_switch_levelling)(const struct vcpu *next);
+extern bool probe_cpuid_faulting(void);
+extern void ctxt_switch_levelling(const struct vcpu *next);
+extern void (*ctxt_switch_masking)(const struct vcpu *next);
 
 extern u64 host_pat;
 extern bool_t opt_cpu_info;