From 42ca8082e260dcfd8afa2afa6ec1940b9d41724c Mon Sep 17 00:00:00 2001

From: Borislav Petkov <bp@suse.de>

Date: Fri, 16 Feb 2018 12:26:40 +0100

Subject: x86/CPU: Check CPU feature bits after microcode upgrade

With some microcode upgrades, new CPUID features can become visible on

the CPU. Check what the kernel has mirrored now and issue a warning

hinting at possible things the user/admin can do to make use of the

newly visible features.

Originally-by: Ashok Raj <ashok.raj@intel.com>

Tested-by: Ashok Raj <ashok.raj@intel.com>

Signed-off-by: Borislav Petkov <bp@suse.de>

Reviewed-by: Ashok Raj <ashok.raj@intel.com>

Cc: Andy Lutomirski <luto@kernel.org>

Cc: Arjan van de Ven <arjan@linux.intel.com>

Cc: Borislav Petkov <bp@alien8.de>

Cc: Dan Williams <dan.j.williams@intel.com>

Cc: Dave Hansen <dave.hansen@linux.intel.com>

Cc: David Woodhouse <dwmw2@infradead.org>

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Cc: Josh Poimboeuf <jpoimboe@redhat.com>

Cc: Linus Torvalds <torvalds@linux-foundation.org>

Cc: Peter Zijlstra <peterz@infradead.org>

Cc: Thomas Gleixner <tglx@linutronix.de>

Link: http://lkml.kernel.org/r/20180216112640.11554-4-bp@alien8.de

Signed-off-by: Ingo Molnar <mingo@kernel.org>

---

 arch/x86/kernel/cpu/common.c | 20 ++++++++++++++++++++

 1 file changed, 20 insertions(+)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c

index 84f1cd8..348cf48 100644

--- a/arch/x86/kernel/cpu/common.c

+++ b/arch/x86/kernel/cpu/common.c

@@ -1757,5 +1757,25 @@ core_initcall(init_cpu_syscore);

  */

 void microcode_check(void)

 {

+	struct cpuinfo_x86 info;

+

 	perf_check_microcode();

+

+	/* Reload CPUID max function as it might've changed. */

+	info.cpuid_level = cpuid_eax(0);

+

+	/*

+	 * Copy all capability leafs to pick up the synthetic ones so that

+	 * memcmp() below doesn't fail on that. The ones coming from CPUID will

+	 * get overwritten in get_cpu_cap().

+	 */

+	memcpy(&info.x86_capability, &boot_cpu_data.x86_capability, sizeof(info.x86_capability));

+

+	get_cpu_cap(&info;;

+

+	if (!memcmp(&info.x86_capability, &boot_cpu_data.x86_capability, sizeof(info.x86_capability)))

+		return;

+

+	pr_warn("x86/CPU: CPU features have changed after loading microcode, but might not take effect.\n");

+	pr_warn("x86/CPU: Please consider either early loading through initrd/built-in or a potential BIOS update.\n");

 }

-- 

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