KVM: selftests: Set input function/index in raw CPUID helper(s)

Set the function/index for CPUID in the helper instead of relying on the
caller to do so.  In addition to reducing the risk of consuming an
uninitialized ECX, having the function/index embedded in the call makes
it easier to understand what is being checked.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-32-seanjc@google.com

tools/testing/selftests/kvm/include/x86_64/processor.h

@@ -404,10 +404,13 @@ static inline void outl(uint16_t port, uint32_t value)
 	__asm__ __volatile__("outl %%eax, %%dx" : : "d"(port), "a"(value));
 }
 
-static inline void cpuid(uint32_t *eax, uint32_t *ebx,
+static inline void __cpuid(uint32_t function, uint32_t index,
+			   uint32_t *eax, uint32_t *ebx,
 			   uint32_t *ecx, uint32_t *edx)
 {
-	/* ecx is often an input as well as an output. */
+	*eax = function;
+	*ecx = index;
+
 	asm volatile("cpuid"
 	    : "=a" (*eax),
 	      "=b" (*ebx),
@@ -417,6 +420,13 @@ static inline void cpuid(uint32_t *eax, uint32_t *ebx,
 	    : "memory");
 }
 
+static inline void cpuid(uint32_t function,
+			 uint32_t *eax, uint32_t *ebx,
+			 uint32_t *ecx, uint32_t *edx)
+{
+	return __cpuid(function, 0, eax, ebx, ecx, edx);
+}
+
 #define SET_XMM(__var, __xmm) \
 	asm volatile("movq %0, %%"#__xmm : : "r"(__var) : #__xmm)
 

tools/testing/selftests/kvm/lib/x86_64/processor.c

@@ -1301,9 +1301,7 @@ unsigned long vm_compute_max_gfn(struct kvm_vm *vm)
 
 	/* Before family 17h, the HyperTransport area is just below 1T.  */
 	ht_gfn = (1 << 28) - num_ht_pages;
-	eax = 1;
-	ecx = 0;
-	cpuid(&eax, &ebx, &ecx, &edx);
+	cpuid(1, &eax, &ebx, &ecx, &edx);
 	if (x86_family(eax) < 0x17)
 		goto done;
 
@@ -1312,18 +1310,15 @@ unsigned long vm_compute_max_gfn(struct kvm_vm *vm)
 	 * reduced due to SME by bits 11:6 of CPUID[0x8000001f].EBX.  Use
 	 * the old conservative value if MAXPHYADDR is not enumerated.
 	 */
-	eax = 0x80000000;
-	cpuid(&eax, &ebx, &ecx, &edx);
+	cpuid(0x80000000, &eax, &ebx, &ecx, &edx);
 	max_ext_leaf = eax;
 	if (max_ext_leaf < 0x80000008)
 		goto done;
 
-	eax = 0x80000008;
-	cpuid(&eax, &ebx, &ecx, &edx);
+	cpuid(0x80000008, &eax, &ebx, &ecx, &edx);
 	max_pfn = (1ULL << ((eax & 0xff) - vm->page_shift)) - 1;
 	if (max_ext_leaf >= 0x8000001f) {
-		eax = 0x8000001f;
-		cpuid(&eax, &ebx, &ecx, &edx);
+		cpuid(0x8000001f, &eax, &ebx, &ecx, &edx);
 		max_pfn >>= (ebx >> 6) & 0x3f;
 	}
 

tools/testing/selftests/kvm/x86_64/amx_test.c

@@ -122,9 +122,7 @@ static inline void check_cpuid_xsave(void)
 {
 	uint32_t eax, ebx, ecx, edx;
 
-	eax = 1;
-	ecx = 0;
-	cpuid(&eax, &ebx, &ecx, &edx);
+	cpuid(1, &eax, &ebx, &ecx, &edx);
 	if (!(ecx & CPUID_XSAVE))
 		GUEST_ASSERT(!"cpuid: no CPU xsave support!");
 	if (!(ecx & CPUID_OSXSAVE))
@@ -140,10 +138,7 @@ static bool enum_xtile_config(void)
 {
 	u32 eax, ebx, ecx, edx;
 
-	eax = TILE_CPUID;
-	ecx = TILE_PALETTE_CPUID_SUBLEAVE;
-
-	cpuid(&eax, &ebx, &ecx, &edx);
+	__cpuid(TILE_CPUID, TILE_PALETTE_CPUID_SUBLEAVE, &eax, &ebx, &ecx, &edx);
 	if (!eax || !ebx || !ecx)
 		return false;
 
@@ -165,10 +160,7 @@ static bool enum_xsave_tile(void)
 {
 	u32 eax, ebx, ecx, edx;
 
-	eax = XSTATE_CPUID;
-	ecx = XFEATURE_XTILEDATA;
-
-	cpuid(&eax, &ebx, &ecx, &edx);
+	__cpuid(XSTATE_CPUID, XFEATURE_XTILEDATA, &eax, &ebx, &ecx, &edx);
 	if (!eax || !ebx)
 		return false;
 
@@ -183,10 +175,7 @@ static bool check_xsave_size(void)
 	u32 eax, ebx, ecx, edx;
 	bool valid = false;
 
-	eax = XSTATE_CPUID;
-	ecx = XSTATE_USER_STATE_SUBLEAVE;
-
-	cpuid(&eax, &ebx, &ecx, &edx);
+	__cpuid(XSTATE_CPUID, XSTATE_USER_STATE_SUBLEAVE, &eax, &ebx, &ecx, &edx);
 	if (ebx && ebx <= XSAVE_SIZE)
 		valid = true;
 

tools/testing/selftests/kvm/x86_64/cpuid_test.c

@@ -31,10 +31,9 @@ static void test_guest_cpuids(struct kvm_cpuid2 *guest_cpuid)
 	u32 eax, ebx, ecx, edx;
 
 	for (i = 0; i < guest_cpuid->nent; i++) {
-		eax = guest_cpuid->entries[i].function;
-		ecx = guest_cpuid->entries[i].index;
-
-		cpuid(&eax, &ebx, &ecx, &edx);
+		__cpuid(guest_cpuid->entries[i].function,
+			guest_cpuid->entries[i].index,
+			&eax, &ebx, &ecx, &edx);
 
 		GUEST_ASSERT(eax == guest_cpuid->entries[i].eax &&
 			     ebx == guest_cpuid->entries[i].ebx &&
@@ -46,9 +45,9 @@ static void test_guest_cpuids(struct kvm_cpuid2 *guest_cpuid)
 
 static void test_cpuid_40000000(struct kvm_cpuid2 *guest_cpuid)
 {
-	u32 eax = 0x40000000, ebx, ecx = 0, edx;
+	u32 eax, ebx, ecx, edx;
 
-	cpuid(&eax, &ebx, &ecx, &edx);
+	cpuid(0x40000000, &eax, &ebx, &ecx, &edx);
 
 	GUEST_ASSERT(eax == 0x40000001);
 }