[PATCH] x86: Report Intel platform_id in /proc/cpuinfo

[Andi Kleen]

From: Andi Kleen <ak@xxxxxxxxxxxxxxx>

We have a need to distinguish systems based on their platform ID.
For example this is useful to distinguish systems with L4 cache
versus ones without.

There is a 3 bit identifier (also called processor flags) in
the IA32_PLATFORM_ID MSR that can give a more fine grained
identification of the CPU than just the model number/stepping.

IA32_PLATFORM_ID is architectural.

The processor flags are already used in the microcode driver.
The MSR can be also accessed through /dev/cpu/*/msr, but that
requires root and is awkward.

This patch just exports the value retrieved by the microcode
driver in /proc/cpuinfo. If the microcode driver is disabled
it won't be shown, but that seems reasonable.

v2: Handle 0 platform_id. Fix commit message.
Cc: hmh@xxxxxxxxxx
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/processor.h      | 2 ++
 arch/x86/kernel/cpu/microcode/intel.c | 2 ++
 arch/x86/kernel/cpu/proc.c            | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 20c11d1..270209c 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -136,6 +136,8 @@ struct cpuinfo_x86 {
 	/* Index into per_cpu list: */
 	u16			cpu_index;
 	u32			microcode;
+	u32			platform_id;
+	u8			has_platform_id;
 };
 
 #define X86_VENDOR_INTEL	0
diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index ee81c54..bcd3f59 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -812,6 +812,8 @@ static int collect_cpu_info(int cpu_num, struct cpu_signature *csig)
 		/* get processor flags from MSR 0x17 */
 		rdmsr(MSR_IA32_PLATFORM_ID, val[0], val[1]);
 		csig->pf = 1 << ((val[1] >> 18) & 7);
+		cpu_data(cpu_num).platform_id = (val[1] >> 18) & 7;
+		cpu_data(cpu_num).has_platform_id = true;
 	}
 
 	csig->rev = c->microcode;
diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 18ca99f..5345d50 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -76,6 +76,8 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 		seq_puts(m, "stepping\t: unknown\n");
 	if (c->microcode)
 		seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
+	if (c->has_platform_id)
+		seq_printf(m, "platform_id\t: %d\n", c->platform_id);
 
 	if (cpu_has(c, X86_FEATURE_TSC)) {
 		unsigned int freq = cpufreq_quick_get(cpu);
-- 
2.8.3