x86/cpuid: Drop get_cpu_vendor() completely

get_cpu_vendor() tries to do a number of things, and ends up doing none of
them well.

For calculating the vendor itself, use x86_cpuid_lookup_vendor() which is
implemented in a far more efficient manner than looping over cpu_devs[].

For setting up this_cpu, set it up once on the BSP only, rather than
latest-takes-precident across the APs.  Such a system is probably not going to
boot, but this feels like a less dangerous course of action.  Adjust the
printed errors to be more clear in the mismatch case.

This removes the only user of cpu_dev->c_ident[], so drop that field as well.

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

xen/arch/x86/cpu/amd.c

@@ -794,7 +794,6 @@ static void init_amd(struct cpuinfo_x86 *c)
 
 static const struct cpu_dev amd_cpu_dev = {
 	.c_vendor	= "AMD",
-	.c_ident 	= { "AuthenticAMD" },
 	.c_early_init	= early_init_amd,
 	.c_init		= init_amd,
 };

xen/arch/x86/cpu/centaur.c

@@ -56,7 +56,6 @@ static void init_centaur(struct cpuinfo_x86 *c)
 
 static const struct cpu_dev centaur_cpu_dev = {
 	.c_vendor	= "Centaur",
-	.c_ident	= { "CentaurHauls" },
 	.c_init		= init_centaur,
 };
 

xen/arch/x86/cpu/common.c

@@ -247,36 +247,6 @@ void display_cacheinfo(struct cpuinfo_x86 *c)
 		       l2size, ecx & 0xFF);
 }
 
-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]) {
-			struct {
-				uint32_t b, d, c;
-			} *ptr = (void *)cpu_devs[i]->c_ident;
-
-			if (ptr->b == b && ptr->c == c && ptr->d == d) {
-				if (mode == gcv_host)
-					this_cpu = cpu_devs[i];
-				return i;
-			}
-		}
-	}
-	if (mode == gcv_guest)
-		return X86_VENDOR_UNKNOWN;
-	if (!printed) {
-		printed++;
-		printk(KERN_ERR "CPU: Vendor unknown, using generic init.\n");
-		printk(KERN_ERR "CPU: Your system may be unstable.\n");
-	}
-	this_cpu = &default_cpu;
-
-	return X86_VENDOR_UNKNOWN;
-}
-
 static inline u32 _phys_pkg_id(u32 cpuid_apic, int index_msb)
 {
 	return cpuid_apic >> index_msb;
@@ -313,7 +283,13 @@ static void __init early_cpu_detect(void)
 	*(u32 *)&c->x86_vendor_id[8] = ecx;
 	*(u32 *)&c->x86_vendor_id[4] = edx;
 
-	c->x86_vendor = get_cpu_vendor(ebx, ecx, edx, gcv_host);
+	c->x86_vendor = x86_cpuid_lookup_vendor(ebx, ecx, edx);
+	if (c->x86_vendor < ARRAY_SIZE(cpu_devs) && cpu_devs[c->x86_vendor])
+		this_cpu = cpu_devs[c->x86_vendor];
+	else
+		printk(XENLOG_ERR
+		       "Unrecognised or unsupported CPU vendor '%.12s'\n",
+		       c->x86_vendor_id);
 
 	cpuid(0x00000001, &eax, &ebx, &ecx, &edx);
 	c->x86 = get_cpu_family(eax, &c->x86_model, &c->x86_mask);
@@ -361,7 +337,12 @@ static void generic_identify(struct cpuinfo_x86 *c)
 	*(u32 *)&c->x86_vendor_id[8] = ecx;
 	*(u32 *)&c->x86_vendor_id[4] = edx;
 
-	c->x86_vendor = get_cpu_vendor(ebx, ecx, edx, gcv_host);
+	c->x86_vendor = x86_cpuid_lookup_vendor(ebx, ecx, edx);
+	if (boot_cpu_data.x86_vendor != c->x86_vendor)
+		printk(XENLOG_ERR "CPU%u vendor %u mismatch against BSP %u\n",
+		       smp_processor_id(), c->x86_vendor,
+		       boot_cpu_data.x86_vendor);
+
 	/* Initialize the standard set of capabilities */
 	/* Note that the vendor-specific code below might override */
 

xen/arch/x86/cpu/cpu.h

@@ -1,7 +1,6 @@
 /* attempt to consolidate cpu attributes */
 struct cpu_dev {
 	char	c_vendor[8];
-	char	c_ident[13];
 
 	void		(*c_early_init)(struct cpuinfo_x86 *c);
 	void		(*c_init)(struct cpuinfo_x86 * c);

xen/arch/x86/cpu/intel.c

@@ -350,7 +350,6 @@ static void init_intel(struct cpuinfo_x86 *c)
 
 static const struct cpu_dev intel_cpu_dev = {
 	.c_vendor	= "Intel",
-	.c_ident 	= { "GenuineIntel" },
 	.c_early_init	= early_init_intel,
 	.c_init		= init_intel,
 };

xen/arch/x86/cpu/shanghai.c

@@ -17,7 +17,6 @@ static void init_shanghai(struct cpuinfo_x86 *c)
 
 static const struct cpu_dev shanghai_cpu_dev = {
     .c_vendor   = "  Shang",
-    .c_ident    = {"  Shanghai  "},
     .c_init     = init_shanghai,
 };
 

xen/arch/x86/cpuid.c

@@ -459,8 +459,8 @@ void recalculate_cpuid_policy(struct domain *d)
     uint32_t fs[FSCAPINTS], max_fs[FSCAPINTS];
     unsigned int i;
 
-    p->x86_vendor = get_cpu_vendor(p->basic.vendor_ebx, p->basic.vendor_ecx,
-                                   p->basic.vendor_edx, gcv_guest);
+    p->x86_vendor = x86_cpuid_lookup_vendor(
+        p->basic.vendor_ebx, p->basic.vendor_ecx, p->basic.vendor_edx);
 
     p->basic.max_leaf   = min(p->basic.max_leaf,   max->basic.max_leaf);
     p->feat.max_subleaf = min(p->feat.max_subleaf, max->feat.max_subleaf);

xen/include/asm-x86/processor.h

@@ -579,13 +579,6 @@ int early_microcode_init(void);
 int microcode_init_intel(void);
 int microcode_init_amd(void);
 
-enum get_cpu_vendor {
-    gcv_host,
-    gcv_guest,
-};
-
-int get_cpu_vendor(uint32_t b, uint32_t c, uint32_t d, enum get_cpu_vendor mode);
-
 static inline uint8_t get_cpu_family(uint32_t raw, uint8_t *model,
                                      uint8_t *stepping)
 {