linux-kernel - [PATCH 2/5] x86/bugs: Separate AMD E400 erratum and C1E bug

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Date:   Fri,  9 Dec 2016 19:29:09 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jiri Olsa <jolsa@...hat.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/5] x86/bugs: Separate AMD E400 erratum and C1E bug

From: Thomas Gleixner <tglx@...utronix.de>

We need two bits of information in order to properly apply the Erratum
400 workaround:

1. X86_BUG_AMD_E400	- to be able to select the proper idle routine
2. X86_BUG_AMD_APIC_C1E - to actually note that the platform we're currently
running on is actually affected by E400.

I say "actually affected" because the bug manifests itself in LAPIC
timer stopping in C1E. But the mere decision whether the platform enters
C1E is made by the firmware. Thus the dancing through hoops we're doing
with this series.

IOW, if the platform firmware decides *not* to enable C1E, we're not
affected even if the CPU f/m/s is among the affected ones - we just
don't enter C1E.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/include/asm/cpufeatures.h |  2 ++
 arch/x86/kernel/cpu/amd.c          | 20 +++++++++++++-------
 arch/x86/kernel/process.c          |  3 +--
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 53e27a12ceb6..eafee3161d1c 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -319,4 +319,6 @@
 #define X86_BUG_NULL_SEG	X86_BUG(10) /* Nulling a selector preserves the base */
 #define X86_BUG_SWAPGS_FENCE	X86_BUG(11) /* SWAPGS without input dep on GS */
 #define X86_BUG_MONITOR		X86_BUG(12) /* IPI required to wake up remote CPU */
+#define X86_BUG_AMD_E400	X86_BUG(13) /* CPU is among the affected by Erratum 400 */
+
 #endif /* _ASM_X86_CPUFEATURES_H */
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 4daad1e39352..71cae73a5076 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -20,6 +20,10 @@
 
 #include "cpu.h"
 
+static const int amd_erratum_383[];
+static const int amd_erratum_400[];
+static bool cpu_has_amd_erratum(struct cpuinfo_x86 *cpu, const int *erratum);
+
 /*
  * nodes_per_socket: Stores the number of nodes per socket.
  * Refer to Fam15h Models 00-0fh BKDG - CPUID Fn8000_001E_ECX
@@ -592,11 +596,16 @@ static void early_init_amd(struct cpuinfo_x86 *c)
 	/* F16h erratum 793, CVE-2013-6885 */
 	if (c->x86 == 0x16 && c->x86_model <= 0xf)
 		msr_set_bit(MSR_AMD64_LS_CFG, 15);
-}
 
-static const int amd_erratum_383[];
-static const int amd_erratum_400[];
-static bool cpu_has_amd_erratum(struct cpuinfo_x86 *cpu, const int *erratum);
+	/*
+	 * Check whether the machine is affected by erratum 400. This is
+	 * used to select the proper idle routine and to enable the check
+	 * whether the machine is affected in arch_post_acpi_init(), which
+	 * sets the X86_BUG_AMD_APIC_C1E bug depending on the MSR check.
+	 */
+	if (cpu_has_amd_erratum(c, amd_erratum_400))
+		set_cpu_bug(c, X86_BUG_AMD_E400);
+}
 
 static void init_amd_k8(struct cpuinfo_x86 *c)
 {
@@ -777,9 +786,6 @@ static void init_amd(struct cpuinfo_x86 *c)
 	if (c->x86 > 0x11)
 		set_cpu_cap(c, X86_FEATURE_ARAT);
 
-	if (cpu_has_amd_erratum(c, amd_erratum_400))
-		set_cpu_bug(c, X86_BUG_AMD_APIC_C1E);
-
 	rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
 
 	/* 3DNow or LM implies PREFETCHW */
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7423acf15b04..bf1a0bab9187 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -402,8 +402,7 @@ void select_idle_routine(const struct cpuinfo_x86 *c)
 	if (x86_idle || boot_option_idle_override == IDLE_POLL)
 		return;
 
-	if (cpu_has_bug(c, X86_BUG_AMD_APIC_C1E)) {
-		/* E400: APIC timer interrupt does not wake up CPU from C1e */
+	if (boot_cpu_has_bug(X86_BUG_AMD_E400)) {
 		pr_info("using AMD E400 aware idle routine\n");
 		x86_idle = amd_e400_idle;
 	} else if (prefer_mwait_c1_over_halt(c)) {
-- 
2.11.0