[PATCH 3/2] x86/microcode/intel: Add a helper which gives the microcode revision

[Borislav Petkov <bp@alien8.de>]

On Wed, Dec 28, 2016 at 12:21:20PM +0100, Borislav Petkov wrote:
> From: Borislav Petkov <bp@suse.de>
> 
> Intel supplies the microcode revision value in MSR 0x8b
> (IA32_BIOS_SIGN_ID) after CPUID(1) has been executed. Execute it each
> time before reading that MSR.

And then, we can go a step further and even do a separate helper which does the
required steps to read out the microcode revision so that we don't forget them
next time we change the code.

Provided that works for xen, though, because I need to do the native
variants but early_init_intel() can call the paravirt *msr() versions
and I have no idea whether that's kosher on xen pv.

Boris, any objections?

---
From: Borislav Petkov <bp@suse.de>
Date: Wed, 28 Dec 2016 13:44:56 +0100
Subject: [PATCH] x86/microcode/intel: Add a helper which gives the microcode
 revision

Since on Intel we're required to do CPUID(1) first, before reading
the microcode revision MSR, let's add a special helper which does the
required steps so that we don't forget to do them next time, when we
want to read the microcode revision.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/include/asm/microcode_intel.h | 15 ++++++++++++
 arch/x86/kernel/cpu/intel.c            | 11 +++------
 arch/x86/kernel/cpu/microcode/intel.c  | 43 ++++++++++------------------------
 3 files changed, 31 insertions(+), 38 deletions(-)

diff --git a/arch/x86/include/asm/microcode_intel.h b/arch/x86/include/asm/microcode_intel.h
index 195becc6f780..e793fc9a9b20 100644
--- a/arch/x86/include/asm/microcode_intel.h
+++ b/arch/x86/include/asm/microcode_intel.h
@@ -52,6 +52,21 @@ struct extended_sigtable {
 
 #define exttable_size(et) ((et)->count * EXT_SIGNATURE_SIZE + EXT_HEADER_SIZE)
 
+static inline u32 intel_get_microcode_revision(void)
+{
+	u32 rev, dummy;
+
+	native_wrmsrl(MSR_IA32_UCODE_REV, 0);
+
+	/* As documented in the SDM: Do a CPUID 1 here */
+	native_cpuid_eax(1);
+
+	/* get the current revision from MSR 0x8B */
+	native_rdmsr(MSR_IA32_UCODE_REV, dummy, rev);
+
+	return rev;
+}
+
 #ifdef CONFIG_MICROCODE_INTEL
 extern void __init load_ucode_intel_bsp(void);
 extern void load_ucode_intel_ap(void);
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 2d49aa949fa1..203f860d2ab3 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -14,6 +14,7 @@
 #include <asm/bugs.h>
 #include <asm/cpu.h>
 #include <asm/intel-family.h>
+#include <asm/microcode_intel.h>
 
 #ifdef CONFIG_X86_64
 #include <linux/topology.h>
@@ -78,14 +79,8 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 		(c->x86 == 0x6 && c->x86_model >= 0x0e))
 		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
 
-	if (c->x86 >= 6 && !cpu_has(c, X86_FEATURE_IA64)) {
-		unsigned lower_word;
-
-		wrmsr(MSR_IA32_UCODE_REV, 0, 0);
-		/* Required by the SDM */
-		native_cpuid_eax(1);
-		rdmsr(MSR_IA32_UCODE_REV, lower_word, c->microcode);
-	}
+	if (c->x86 >= 6 && !cpu_has(c, X86_FEATURE_IA64))
+		c->microcode = intel_get_microcode_revision();
 
 	/*
 	 * Atom erratum AAE44/AAF40/AAG38/AAH41:
diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index f79249fab389..faec8fa68ffd 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -390,15 +390,8 @@ static int collect_cpu_info_early(struct ucode_cpu_info *uci)
 		native_rdmsr(MSR_IA32_PLATFORM_ID, val[0], val[1]);
 		csig.pf = 1 << ((val[1] >> 18) & 7);
 	}
-	native_wrmsrl(MSR_IA32_UCODE_REV, 0);
 
-	/* As documented in the SDM: Do a CPUID 1 here */
-	native_cpuid_eax(1);
-
-	/* get the current revision from MSR 0x8B */
-	native_rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
-
-	csig.rev = val[1];
+	csig.rev = intel_get_microcode_revision();
 
 	uci->cpu_sig = csig;
 	uci->valid = 1;
@@ -582,7 +575,7 @@ static inline void print_ucode(struct ucode_cpu_info *uci)
 static int apply_microcode_early(struct ucode_cpu_info *uci, bool early)
 {
 	struct microcode_intel *mc;
-	unsigned int val[2];
+	u32 rev;
 
 	mc = uci->mc;
 	if (!mc)
@@ -590,21 +583,16 @@ static int apply_microcode_early(struct ucode_cpu_info *uci, bool early)
 
 	/* write microcode via MSR 0x79 */
 	native_wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);
-	native_wrmsrl(MSR_IA32_UCODE_REV, 0);
 
-	/* As documented in the SDM: Do a CPUID 1 here */
-	native_cpuid_eax(1);
-
-	/* get the current revision from MSR 0x8B */
-	native_rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
-	if (val[1] != mc->hdr.rev)
+	rev = intel_get_microcode_revision();
+	if (rev != mc->hdr.rev)
 		return -1;
 
 #ifdef CONFIG_X86_64
 	/* Flush global tlb. This is precaution. */
 	flush_tlb_early();
 #endif
-	uci->cpu_sig.rev = val[1];
+	uci->cpu_sig.rev = rev;
 
 	if (early)
 		print_ucode(uci);
@@ -784,8 +772,8 @@ static int apply_microcode_intel(int cpu)
 	struct microcode_intel *mc;
 	struct ucode_cpu_info *uci;
 	struct cpuinfo_x86 *c;
-	unsigned int val[2];
 	static int prev_rev;
+	u32 rev;
 
 	/* We should bind the task to the CPU */
 	if (WARN_ON(raw_smp_processor_id() != cpu))
@@ -802,33 +790,28 @@ static int apply_microcode_intel(int cpu)
 
 	/* write microcode via MSR 0x79 */
 	wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);
-	wrmsrl(MSR_IA32_UCODE_REV, 0);
-
-	/* As documented in the SDM: Do a CPUID 1 here */
-	native_cpuid_eax(1);
 
-	/* get the current revision from MSR 0x8B */
-	rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
+	rev = intel_get_microcode_revision();
 
-	if (val[1] != mc->hdr.rev) {
+	if (rev != mc->hdr.rev) {
 		pr_err("CPU%d update to revision 0x%x failed\n",
 		       cpu, mc->hdr.rev);
 		return -1;
 	}
 
-	if (val[1] != prev_rev) {
+	if (rev != prev_rev) {
 		pr_info("updated to revision 0x%x, date = %04x-%02x-%02x\n",
-			val[1],
+			rev,
 			mc->hdr.date & 0xffff,
 			mc->hdr.date >> 24,
 			(mc->hdr.date >> 16) & 0xff);
-		prev_rev = val[1];
+		prev_rev = rev;
 	}
 
 	c = &cpu_data(cpu);
 
-	uci->cpu_sig.rev = val[1];
-	c->microcode = val[1];
+	uci->cpu_sig.rev = rev;
+	c->microcode = rev;
 
 	return 0;
 }
-- 
2.8.4

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--