KVM: x86: Add dedicated helper to get CPUID entry with significant index

Add a second CPUID helper, kvm_find_cpuid_entry_index(), to handle KVM
queries for CPUID leaves whose index _may_ be significant, and drop the
index param from the existing kvm_find_cpuid_entry().  Add a WARN in the
inner helper, cpuid_entry2_find(), to detect attempts to retrieve a CPUID
entry whose index is significant without explicitly providing an index.

Using an explicit magic number and letting callers omit the index avoids
confusion by eliminating the myriad cases where KVM specifies '0' as a
dummy value.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 60 insertions, 20 deletions

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index d47222ab8e6e..75dcf7a72605 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -67,9 +67,17 @@ u32 xstate_required_size(u64 xstate_bv, bool compacted)
 #define F feature_bit
 #define SF(name) (boot_cpu_has(X86_FEATURE_##name) ? F(name) : 0)
 
+/*
+ * Magic value used by KVM when querying userspace-provided CPUID entries and
+ * doesn't care about the CPIUD index because the index of the function in
+ * question is not significant.  Note, this magic value must have at least one
+ * bit set in bits[63:32] and must be consumed as a u64 by cpuid_entry2_find()
+ * to avoid false positives when processing guest CPUID input.
+ */
+#define KVM_CPUID_INDEX_NOT_SIGNIFICANT -1ull
 
 static inline struct kvm_cpuid_entry2 *cpuid_entry2_find(
-	struct kvm_cpuid_entry2 *entries, int nent, u32 function, u32 index)
+	struct kvm_cpuid_entry2 *entries, int nent, u32 function, u64 index)
 {
 	struct kvm_cpuid_entry2 *e;
 	int i;
@@ -77,9 +85,31 @@ static inline struct kvm_cpuid_entry2 *cpuid_entry2_find(
 	for (i = 0; i < nent; i++) {
 		e = &entries[i];
 
-		if (e->function == function &&
-		    (!(e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX) || e->index == index))
+		if (e->function != function)
+			continue;
+
+		/*
+		 * If the index isn't significant, use the first entry with a
+		 * matching function.  It's userspace's responsibilty to not
+		 * provide "duplicate" entries in all cases.
+		 */
+		if (!(e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX) || e->index == index)
+			return e;
+
+
+		/*
+		 * Similarly, use the first matching entry if KVM is doing a
+		 * lookup (as opposed to emulating CPUID) for a function that's
+		 * architecturally defined as not having a significant index.
+		 */
+		if (index == KVM_CPUID_INDEX_NOT_SIGNIFICANT) {
+			/*
+			 * Direct lookups from KVM should not diverge from what
+			 * KVM defines internally (the architectural behavior).
+			 */
+			WARN_ON_ONCE(cpuid_function_is_indexed(function));
 			return e;
+		}
 	}
 
 	return NULL;
@@ -96,7 +126,8 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
 	 * The existing code assumes virtual address is 48-bit or 57-bit in the
 	 * canonical address checks; exit if it is ever changed.
 	 */
-	best = cpuid_entry2_find(entries, nent, 0x80000008, 0);
+	best = cpuid_entry2_find(entries, nent, 0x80000008,
+				 KVM_CPUID_INDEX_NOT_SIGNIFICANT);
 	if (best) {
 		int vaddr_bits = (best->eax & 0xff00) >> 8;
 
@@ -151,7 +182,7 @@ static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu)
 	vcpu->arch.kvm_cpuid_base = 0;
 
 	for_each_possible_hypervisor_cpuid_base(function) {
-		entry = kvm_find_cpuid_entry(vcpu, function, 0);
+		entry = kvm_find_cpuid_entry(vcpu, function);
 
 		if (entry) {
 			u32 signature[3];
@@ -177,7 +208,8 @@ static struct kvm_cpuid_entry2 *__kvm_find_kvm_cpuid_features(struct kvm_vcpu *v
 	if (!base)
 		return NULL;
 
-	return cpuid_entry2_find(entries, nent, base | KVM_CPUID_FEATURES, 0);
+	return cpuid_entry2_find(entries, nent, base | KVM_CPUID_FEATURES,
+				 KVM_CPUID_INDEX_NOT_SIGNIFICANT);
 }
 
 static struct kvm_cpuid_entry2 *kvm_find_kvm_cpuid_features(struct kvm_vcpu *vcpu)
@@ -219,7 +251,7 @@ static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_e
 	struct kvm_cpuid_entry2 *best;
 	u64 guest_supported_xcr0 = cpuid_get_supported_xcr0(entries, nent);
 
-	best = cpuid_entry2_find(entries, nent, 1, 0);
+	best = cpuid_entry2_find(entries, nent, 1, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
 	if (best) {
 		/* Update OSXSAVE bit */
 		if (boot_cpu_has(X86_FEATURE_XSAVE))
@@ -250,7 +282,7 @@ static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_e
 		best->eax &= ~(1 << KVM_FEATURE_PV_UNHALT);
 
 	if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT)) {
-		best = cpuid_entry2_find(entries, nent, 0x1, 0);
+		best = cpuid_entry2_find(entries, nent, 0x1, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
 		if (best)
 			cpuid_entry_change(best, X86_FEATURE_MWAIT,
 					   vcpu->arch.ia32_misc_enable_msr &
@@ -285,7 +317,7 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	struct kvm_cpuid_entry2 *best;
 	u64 guest_supported_xcr0;
 
-	best = kvm_find_cpuid_entry(vcpu, 1, 0);
+	best = kvm_find_cpuid_entry(vcpu, 1);
 	if (best && apic) {
 		if (cpuid_entry_has(best, X86_FEATURE_TSC_DEADLINE_TIMER))
 			apic->lapic_timer.timer_mode_mask = 3 << 17;
@@ -325,10 +357,10 @@ int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpuid_entry2 *best;
 
-	best = kvm_find_cpuid_entry(vcpu, 0x80000000, 0);
+	best = kvm_find_cpuid_entry(vcpu, 0x80000000);
 	if (!best || best->eax < 0x80000008)
 		goto not_found;
-	best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
+	best = kvm_find_cpuid_entry(vcpu, 0x80000008);
 	if (best)
 		return best->eax & 0xff;
 not_found:
@@ -1302,12 +1334,20 @@ out_free:
 	return r;
 }
 
-struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
-					      u32 function, u32 index)
+struct kvm_cpuid_entry2 *kvm_find_cpuid_entry_index(struct kvm_vcpu *vcpu,
+						    u32 function, u32 index)
 {
 	return cpuid_entry2_find(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent,
 				 function, index);
 }
+EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry_index);
+
+struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
+					      u32 function)
+{
+	return cpuid_entry2_find(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent,
+				 function, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
+}
 EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry);
 
 /*
@@ -1344,7 +1384,7 @@ get_out_of_range_cpuid_entry(struct kvm_vcpu *vcpu, u32 *fn_ptr, u32 index)
 	struct kvm_cpuid_entry2 *basic, *class;
 	u32 function = *fn_ptr;
 
-	basic = kvm_find_cpuid_entry(vcpu, 0, 0);
+	basic = kvm_find_cpuid_entry(vcpu, 0);
 	if (!basic)
 		return NULL;
 
@@ -1353,11 +1393,11 @@ get_out_of_range_cpuid_entry(struct kvm_vcpu *vcpu, u32 *fn_ptr, u32 index)
 		return NULL;
 
 	if (function >= 0x40000000 && function <= 0x4fffffff)
-		class = kvm_find_cpuid_entry(vcpu, function & 0xffffff00, 0);
+		class = kvm_find_cpuid_entry(vcpu, function & 0xffffff00);
 	else if (function >= 0xc0000000)
-		class = kvm_find_cpuid_entry(vcpu, 0xc0000000, 0);
+		class = kvm_find_cpuid_entry(vcpu, 0xc0000000);
 	else
-		class = kvm_find_cpuid_entry(vcpu, function & 0x80000000, 0);
+		class = kvm_find_cpuid_entry(vcpu, function & 0x80000000);
 
 	if (class && function <= class->eax)
 		return NULL;
@@ -1375,7 +1415,7 @@ get_out_of_range_cpuid_entry(struct kvm_vcpu *vcpu, u32 *fn_ptr, u32 index)
 	 * the effective CPUID entry is the max basic leaf.  Note, the index of
 	 * the original requested leaf is observed!
 	 */
-	return kvm_find_cpuid_entry(vcpu, basic->eax, index);
+	return kvm_find_cpuid_entry_index(vcpu, basic->eax, index);
 }
 
 bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
@@ -1385,7 +1425,7 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 	struct kvm_cpuid_entry2 *entry;
 	bool exact, used_max_basic = false;
 
-	entry = kvm_find_cpuid_entry(vcpu, function, index);
+	entry = kvm_find_cpuid_entry_index(vcpu, function, index);
 	exact = !!entry;
 
 	if (!entry && !exact_only) {
@@ -1414,7 +1454,7 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 		 * exists. EDX can be copied from any existing index.
 		 */
 		if (function == 0xb || function == 0x1f) {
-			entry = kvm_find_cpuid_entry(vcpu, function, 1);
+			entry = kvm_find_cpuid_entry_index(vcpu, function, 1);
 			if (entry) {
 				*ecx = index & 0xff;
 				*edx = entry->edx;