re-enable AMD Topology extension on certain models if disabled by BIOS

Some BIOSes disable AMD Topology extension on AMD Family 15h notebook
processors.  We re-enable the extension, so that we can properly discover
core and cache topology.  Linux seems to do the same.

Reported by:	Johannes Dieterich <dieterich.joh@gmail.com>
Reviewed by:	jhb, kib
Tested by:	Johannes Dieterich <dieterich.joh@gmail.com>
		(earlier version)
MFC after:	3 weeks
Differential Revision:	https://reviews.freebsd.org/D5883

3 files changed, 29 insertions, 13 deletions

diff --git a/sys/x86/include/specialreg.h b/sys/x86/include/specialreg.h
index c2d2c59..5f71b2d 100644
--- a/sys/x86/include/specialreg.h
+++ b/sys/x86/include/specialreg.h
@@ -816,6 +816,7 @@
 #define	MSR_P_STATE_CONFIG(n) (0xc0010064 + (n)) /* P-state Config */
 #define	MSR_SMM_ADDR	0xc0010112	/* SMM TSEG base address */
 #define	MSR_SMM_MASK	0xc0010113	/* SMM TSEG address mask */
+#define	MSR_EXTFEATURES	0xc0011005	/* Extended CPUID Features override */
 #define	MSR_IC_CFG	0xc0011021	/* Instruction Cache Configuration */
 #define	MSR_K8_UCODE_UPDATE	0xc0010020	/* update microcode */
 #define	MSR_MC0_CTL_MASK	0xc0010044
diff --git a/sys/x86/include/x86_var.h b/sys/x86/include/x86_var.h
index 46ce1a0..07e9d80 100644
--- a/sys/x86/include/x86_var.h
+++ b/sys/x86/include/x86_var.h
@@ -103,7 +103,7 @@ void	dump_drop_page(vm_paddr_t);
 void	identify_cpu(void);
 void	initializecpu(void);
 void	initializecpucache(void);
-bool	intel_fix_cpuid(void);
+bool	fix_cpuid(void);
 void	fillw(int /*u_short*/ pat, void *base, size_t cnt);
 int	is_physical_memory(vm_paddr_t addr);
 int	isa_nmi(int cd);
diff --git a/sys/x86/x86/identcpu.c b/sys/x86/x86/identcpu.c
index bc232a2..41ba36a 100644
--- a/sys/x86/x86/identcpu.c
+++ b/sys/x86/x86/identcpu.c
@@ -1342,23 +1342,22 @@ identify_hypervisor(void)
 	}
 }
 
-/*
- * Clear "Limit CPUID Maxval" bit and return true if the caller should
- * get the largest standard CPUID function number again if it is set
- * from BIOS.  It is necessary for probing correct CPU topology later
- * and for the correct operation of the AVX-aware userspace.
- */
 bool
-intel_fix_cpuid(void)
+fix_cpuid(void)
 {
 	uint64_t msr;
 
-	if (cpu_vendor_id != CPU_VENDOR_INTEL)
-		return (false);
-	if ((CPUID_TO_FAMILY(cpu_id) == 0xf &&
+	/*
+	 * Clear "Limit CPUID Maxval" bit and return true if the caller should
+	 * get the largest standard CPUID function number again if it is set
+	 * from BIOS.  It is necessary for probing correct CPU topology later
+	 * and for the correct operation of the AVX-aware userspace.
+	 */
+	if (cpu_vendor_id == CPU_VENDOR_INTEL &&
+	    ((CPUID_TO_FAMILY(cpu_id) == 0xf &&
 	    CPUID_TO_MODEL(cpu_id) >= 0x3) ||
 	    (CPUID_TO_FAMILY(cpu_id) == 0x6 &&
-	    CPUID_TO_MODEL(cpu_id) >= 0xe)) {
+	    CPUID_TO_MODEL(cpu_id) >= 0xe))) {
 		msr = rdmsr(MSR_IA32_MISC_ENABLE);
 		if ((msr & IA32_MISC_EN_LIMCPUID) != 0) {
 			msr &= ~IA32_MISC_EN_LIMCPUID;
@@ -1366,6 +1365,22 @@ intel_fix_cpuid(void)
 			return (true);
 		}
 	}
+
+	/*
+	 * Re-enable AMD Topology Extension that could be disabled by BIOS
+	 * on some notebook processors.  Without the extension it's really
+	 * hard to determine the correct CPU cache topology.
+	 * See BIOS and Kernel Developer’s Guide (BKDG) for AMD Family 15h
+	 * Models 60h-6Fh Processors, Publication # 50742.
+	 */
+	if (cpu_vendor_id == CPU_VENDOR_AMD && CPUID_TO_FAMILY(cpu_id) == 0x15) {
+		msr = rdmsr(MSR_EXTFEATURES);
+		if ((msr & ((uint64_t)1 << 54)) == 0) {
+			msr |= (uint64_t)1 << 54;
+			wrmsr(MSR_EXTFEATURES, msr);
+			return (true);
+		}
+	}
 	return (false);
 }
 
@@ -1403,7 +1418,7 @@ identify_cpu(void)
 	identify_hypervisor();
 	cpu_vendor_id = find_cpu_vendor_id();
 
-	if (intel_fix_cpuid()) {
+	if (fix_cpuid()) {
 		do_cpuid(0, regs);
 		cpu_high = regs[0];
 	}