[PATCH 25/26] KVM: x86: Handle main Intel PT CPUID leaf in vendor code

[Sean Christopherson]

Move the clearing of the Intel PT CPUID leaf into vendor code to
eliminate a call to ->pt_supported().  To handle clearing CPUID 0x14's
index>0 sub-leafs, introduce the pattern of adding feature-dependent
sub-leafs (index>0 sub-leafs whose existence is enumerated by index=0)
after calling ->set_supported_cpuid().  The dependent sub-leafs pattern
can be reused for future (Intel) features such as SGX to allow vendor
code to disable the feature, e.g. via module param, without having to
add a feature specific kvm_x86_ops hook.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 arch/x86/kvm/cpuid.c   | 32 ++++++++++++++++----------------
 arch/x86/kvm/svm.c     |  3 +++
 arch/x86/kvm/vmx/vmx.c |  4 ++++
 3 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index d06fb54c9c0d..ca766c460318 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -409,7 +409,6 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 	unsigned f_gbpages = 0;
 	unsigned f_lm = 0;
 #endif
-	unsigned f_intel_pt = kvm_x86_ops->pt_supported() ? F(INTEL_PT) : 0;
 
 	/* cpuid 1.edx */
 	const u32 kvm_cpuid_1_edx_x86_features =
@@ -648,22 +647,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 		break;
 	}
 	/* Intel PT */
-	case 0x14: {
-		int t, times = entry->eax;
-
-		if (!f_intel_pt) {
-			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
-			break;
-		}
-
-		for (t = 1; t <= times; ++t) {
-			if (*nent >= maxnent)
-				goto out;
-			do_host_cpuid(&entry[t], function, t);
-			++*nent;
-		}
+	case 0x14:
 		break;
-	}
 	case KVM_CPUID_SIGNATURE: {
 		static const char signature[12] = "KVMKVMKVM\0\0";
 		const u32 *sigptr = (const u32 *)signature;
@@ -778,6 +763,21 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 
 	kvm_x86_ops->set_supported_cpuid(entry);
 
+	/*
+	 * Add feature-dependent sub-leafs after ->set_supported_cpuid() to
+	 * properly handle the feature being disabled by SVM/VMX.
+	 */
+	if (function == 0x14) {
+		int t, times = entry->eax;
+
+		for (t = 1; t <= times; ++t) {
+			if (*nent >= maxnent)
+				goto out;
+			do_host_cpuid(&entry[t], function, t);
+			++*nent;
+		}
+	}
+
 	r = 0;
 
 out:
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 350cdf91a576..a08ee7b2dddb 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -6068,6 +6068,9 @@ static void svm_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
 		cpuid_entry_clear(entry, X86_FEATURE_INVPCID);
 		cpuid_entry_clear(entry, X86_FEATURE_INTEL_PT);
 		break;
+	case 0x14:
+		entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+		break;
 	case 0x80000001:
 		if (nested)
 			cpuid_entry_set(entry, X86_FEATURE_SVM);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 35134dbed2f0..10c31aa40730 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7155,6 +7155,10 @@ static void vmx_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
 		if (vmx_umip_emulated())
 			cpuid_entry_set(entry, X86_FEATURE_UMIP);
 		break;
+	case 0x14:
+		if (!vmx_pt_mode_is_host_guest())
+			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+		break;
 	case 0x80000001:
 		if (!cpu_has_vmx_rdtscp())
 			cpuid_entry_clear(entry, X86_FEATURE_RDTSCP);
-- 
2.24.1