[RFC PATCH 01/11] x86: Add more granularity to the vendors in Kconfig

[Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>]

This enables very aggressive DCE passes on single-vendor builds in later
patches, as it will allow most vendor checks to become statically chosen
branches. A lot of statics go away and a lot more inlining is allowed.

In order to allow x86_vendor_is() to fold into constants, expand Kconfig
to have the full set of vendors. Adds Hygon, Centaur, Shanghai and the
default path.

Have Hygon depend on AMD, and Centaur+Shanghai depend on Intel.

Not a functional change.

Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
---
 xen/arch/x86/Kconfig.cpu         | 45 ++++++++++++++++++++++++++++++++
 xen/arch/x86/cpu/common.c        | 17 +++++++-----
 xen/arch/x86/include/asm/cpuid.h |  7 +++++
 3 files changed, 62 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/Kconfig.cpu b/xen/arch/x86/Kconfig.cpu
index 5fb18db1aa..aaf70fb37b 100644
--- a/xen/arch/x86/Kconfig.cpu
+++ b/xen/arch/x86/Kconfig.cpu
@@ -19,4 +19,49 @@ config INTEL
          May be turned off in builds targetting other vendors.  Otherwise,
          must be enabled for Xen to work suitably on Intel platforms.
 
+config HYGON
+       bool "Support Hygon CPUs"
+       depends on AMD
+       default y
+       help
+         Detection, tunings and quirks for Hygon platforms.
+
+         May be turned off in builds targetting other vendors.  Otherwise,
+         must be enabled for Xen to work suitably on Hygon platforms.
+
+
+config CENTAUR
+       bool "Support Centaur CPUs"
+       depends on INTEL
+       default y
+       help
+         Detection, tunings and quirks for Centaur platforms.
+
+         May be turned off in builds targetting other vendors.  Otherwise,
+         must be enabled for Xen to work suitably on Centaur platforms.
+
+config SHANGHAI
+       bool "Support Shanghai CPUs"
+       depends on INTEL
+       default y
+       help
+         Detection, tunings and quirks for Shanghai platforms.
+
+         May be turned off in builds targetting other vendors.  Otherwise,
+         must be enabled for Xen to work suitably on Shanghai platforms.
+
+config UNKNOWN_CPU
+       bool "Support unknown CPUs"
+       default y
+       help
+         This option prevents a panic on boot when the host CPU vendor isn't
+         supported by going into a legacy compatibility mode and not applying
+         any relevant tunings or quirks.
+
+         Not selecting this options while selecting multiple vendors doesn't 
have
+         any major effect on code size, but while selecting a single vendor
+         it produces a smaller build especially optimised for size.
+
+         If unsure, say Y.
+
 endmenu
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 37820a3a08..393c30227f 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -118,7 +118,7 @@ static void cf_check default_init(struct cpuinfo_x86 * c)
        __clear_bit(X86_FEATURE_SEP, c->x86_capability);
 }
 
-static const struct cpu_dev __initconst_cf_clobber __used default_cpu = {
+static const struct cpu_dev __initconst_cf_clobber default_cpu = {
        .c_init = default_init,
 };
 static struct cpu_dev __ro_after_init actual_cpu;
@@ -340,7 +340,8 @@ void __init early_cpu_init(bool verbose)
        *(u32 *)&c->x86_vendor_id[8] = ecx;
        *(u32 *)&c->x86_vendor_id[4] = edx;
 
-       c->x86_vendor = x86_cpuid_lookup_vendor(ebx, ecx, edx);
+       c->x86_vendor = x86_cpuid_lookup_vendor(ebx, ecx, edx) &
+                       X86_ENABLED_VENDORS;
        switch (c->x86_vendor) {
        case X86_VENDOR_INTEL:    intel_unlock_cpuid_leaves(c);
                                  actual_cpu = intel_cpu_dev;    break;
@@ -349,12 +350,14 @@ void __init early_cpu_init(bool verbose)
        case X86_VENDOR_SHANGHAI: actual_cpu = shanghai_cpu_dev; break;
        case X86_VENDOR_HYGON:    actual_cpu = hygon_cpu_dev;    break;
        default:
+               if (verbose || !IS_ENABLED(CONFIG_UNKNOWN_CPU))
+                       printk(XENLOG_ERR
+                              "Unrecognised or unsupported CPU vendor 
'%.12s'\n",
+                              c->x86_vendor_id);
+               if (!IS_ENABLED(CONFIG_UNKNOWN_CPU))
+                       panic("Cannot run in unknown/compiled-out CPU 
vendor.\n");
+
                actual_cpu = default_cpu;
-               if (!verbose)
-                       break;
-               printk(XENLOG_ERR
-                      "Unrecognised or unsupported CPU vendor '%.12s'\n",
-                      c->x86_vendor_id);
        }
 
        cpuid(0x00000001, &eax, &ebx, &ecx, &edx);
diff --git a/xen/arch/x86/include/asm/cpuid.h b/xen/arch/x86/include/asm/cpuid.h
index f1b9e37a42..bf1c635cdd 100644
--- a/xen/arch/x86/include/asm/cpuid.h
+++ b/xen/arch/x86/include/asm/cpuid.h
@@ -49,6 +49,13 @@ struct cpuid_leaf;
 void guest_cpuid(const struct vcpu *v, uint32_t leaf,
                  uint32_t subleaf, struct cpuid_leaf *res);
 
+#define X86_ENABLED_VENDORS \
+    ((IS_ENABLED(CONFIG_INTEL)    ? X86_VENDOR_INTEL    : 0) | \
+     (IS_ENABLED(CONFIG_AMD)      ? X86_VENDOR_AMD      : 0) | \
+     (IS_ENABLED(CONFIG_CENTAUR)  ? X86_VENDOR_CENTAUR  : 0) | \
+     (IS_ENABLED(CONFIG_SHANGHAI) ? X86_VENDOR_SHANGHAI : 0) | \
+     (IS_ENABLED(CONFIG_HYGON)    ? X86_VENDOR_HYGON    : 0))
+
 #endif /* !__X86_CPUID_H__ */
 
 /*
-- 
2.43.0