x86/cpu: Improvements to get_cpu_vendor()

Comparing 3 integers is more efficient than using strcmp(), and is more useful
to the gcv_guest case than having to fabricate a suitable string to pass.  The
gcv_host cases have both options easily to hand, and experimentally, the
resulting code is more efficient.

Update the cpu_dev structure to be more efficient.  c_vendor[] only needs to
be 8 bytes long to cover all the CPU drivers Xen has, which avoids storing an
8-byte pointer to 8 bytes of data.  Drop c_ident[1] as we have no CPU drivers
with a second ident string, and turn it into an anonymous union to allow
access to the integer values directly.

This avoids all need for the vendor_id union in update_domain_cpuid_info().

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/cpu/common.c

@@ -156,16 +156,15 @@ void display_cacheinfo(struct cpuinfo_x86 *c)
 		       l2size, ecx & 0xFF);
 }
 
-int get_cpu_vendor(const char v[], enum get_cpu_vendor mode)
+int get_cpu_vendor(uint32_t b, uint32_t c, uint32_t d, enum get_cpu_vendor mode)
 {
 	int i;
 	static int printed;
 
 	for (i = 0; i < X86_VENDOR_NUM; i++) {
 		if (cpu_devs[i]) {
-			if (!strcmp(v,cpu_devs[i]->c_ident[0]) ||
-			    (cpu_devs[i]->c_ident[1] && 
-			     !strcmp(v,cpu_devs[i]->c_ident[1]))) {
+			if (cpu_devs[i]->b == b && cpu_devs[i]->c == c &&
+			    cpu_devs[i]->d == d) {
 				if (mode == gcv_host)
 					this_cpu = cpu_devs[i];
 				return i;
@@ -234,12 +233,12 @@ static void __init early_cpu_detect(void)
 	c->x86_cache_alignment = 32;
 
 	/* Get vendor name */
-	cpuid(0x00000000, &c->cpuid_level,
-	      (int *)&c->x86_vendor_id[0],
-	      (int *)&c->x86_vendor_id[8],
-	      (int *)&c->x86_vendor_id[4]);
+	cpuid(0x00000000, &c->cpuid_level, &ebx, &ecx, &edx);
+	*(u32 *)&c->x86_vendor_id[0] = ebx;
+	*(u32 *)&c->x86_vendor_id[8] = ecx;
+	*(u32 *)&c->x86_vendor_id[4] = edx;
 
-	c->x86_vendor = get_cpu_vendor(c->x86_vendor_id, gcv_host);
+	c->x86_vendor = get_cpu_vendor(ebx, ecx, edx, gcv_host);
 
 	cpuid(0x00000001, &eax, &ebx, &ecx, &edx);
 	c->x86 = get_cpu_family(eax, &c->x86_model, &c->x86_mask);
@@ -277,12 +276,12 @@ static void generic_identify(struct cpuinfo_x86 *c)
 	u32 eax, ebx, ecx, edx, tmp;
 
 	/* Get vendor name */
-	cpuid(0x00000000, &c->cpuid_level,
-	      (int *)&c->x86_vendor_id[0],
-	      (int *)&c->x86_vendor_id[8],
-	      (int *)&c->x86_vendor_id[4]);
+	cpuid(0x00000000, &c->cpuid_level, &ebx, &ecx, &edx);
+	*(u32 *)&c->x86_vendor_id[0] = ebx;
+	*(u32 *)&c->x86_vendor_id[8] = ecx;
+	*(u32 *)&c->x86_vendor_id[4] = edx;
 
-	c->x86_vendor = get_cpu_vendor(c->x86_vendor_id, gcv_host);
+	c->x86_vendor = get_cpu_vendor(ebx, ecx, edx, gcv_host);
 	/* Initialize the standard set of capabilities */
 	/* Note that the vendor-specific code below might override */
 

xen/arch/x86/cpu/cpu.h

@@ -1,9 +1,13 @@
 /* attempt to consolidate cpu attributes */
 struct cpu_dev {
-	char	* c_vendor;
+	char	c_vendor[8];
 
-	/* some have two possibilities for cpuid string */
-	char	* c_ident[2];	
+	union {
+		char	c_ident[13];
+		struct {
+			uint32_t b, d, c;
+		};
+	};
 
 	void		(*c_early_init)(struct cpuinfo_x86 *c);
 	void		(*c_init)(struct cpuinfo_x86 * c);

xen/arch/x86/domctl.c

@@ -54,21 +54,10 @@ static void update_domain_cpuid_info(struct domain *d,
     switch ( ctl->input[0] )
     {
     case 0: {
-        union {
-            typeof(boot_cpu_data.x86_vendor_id) str;
-            struct {
-                uint32_t ebx, edx, ecx;
-            } reg;
-        } vendor_id = {
-            .reg = {
-                .ebx = ctl->ebx,
-                .edx = ctl->edx,
-                .ecx = ctl->ecx
-            }
-        };
         int old_vendor = d->arch.x86_vendor;
 
-        d->arch.x86_vendor = get_cpu_vendor(vendor_id.str, gcv_guest);
+        d->arch.x86_vendor = get_cpu_vendor(
+            ctl->ebx, ctl->ecx, ctl->edx, gcv_guest);
 
         if ( is_hvm_domain(d) && (d->arch.x86_vendor != old_vendor) )
         {

xen/include/asm-x86/processor.h

@@ -624,7 +624,7 @@ enum get_cpu_vendor {
     gcv_guest,
 };
 
-int get_cpu_vendor(const char vendor_id[], enum get_cpu_vendor);
+int get_cpu_vendor(uint32_t b, uint32_t c, uint32_t d, enum get_cpu_vendor mode);
 uint8_t get_cpu_family(uint32_t raw, uint8_t *model, uint8_t *stepping);
 
 void pv_cpuid(struct cpu_user_regs *regs);