linux-kernel - [PATCH] x86/CPU: Sync CPU feature flags late

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Message-Id: <20180109231739.4681-1-bp@alien8.de>
Date:   Wed, 10 Jan 2018 00:17:39 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] x86/CPU: Sync CPU feature flags late

From: Borislav Petkov <bp@...e.de>

This is for the case where we need to set feature flags late, like, for
example, after late microcode patch has been loaded which has enabled
new CPUID bits.

This has no effect on alternatives patching.

Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org
---
 arch/x86/kernel/cpu/common.c | 17 +++++++++++++++++
 arch/x86/kernel/cpu/cpu.h    |  3 +++
 2 files changed, 20 insertions(+)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 372ba3fb400f..7a884c518879 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -724,6 +724,23 @@ static void apply_forced_caps(struct cpuinfo_x86 *c)
 	}
 }
 
+/*
+ * This late synchronization of CPU caps has no effect on alternatives patching
+ * but updates the visible feature bits per CPU.
+ */
+void cpu_caps_sync_late(void)
+{
+	int cpu;
+
+	lockdep_assert_cpus_held();
+
+	for_each_online_cpu(cpu) {
+		struct cpuinfo_x86 *c = &cpu_data(cpu);
+
+		apply_forced_caps(c);
+	}
+}
+
 void get_cpu_cap(struct cpuinfo_x86 *c)
 {
 	u32 eax, ebx, ecx, edx;
diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h
index f52a370b6c00..8bb2d1fe6d1d 100644
--- a/arch/x86/kernel/cpu/cpu.h
+++ b/arch/x86/kernel/cpu/cpu.h
@@ -46,5 +46,8 @@ extern const struct cpu_dev *const __x86_cpu_dev_start[],
 			    *const __x86_cpu_dev_end[];
 
 extern void get_cpu_cap(struct cpuinfo_x86 *c);
+
+extern void cpu_caps_sync_late(void);
+
 extern void cpu_detect_cache_sizes(struct cpuinfo_x86 *c);
 #endif /* ARCH_X86_CPU_H */
-- 
2.13.0