linux-kernel - [tip:x86/pti] x86/CPU: Check CPU feature bits after microcode upgrade

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Message-ID: <tip-42ca8082e260dcfd8afa2afa6ec1940b9d41724c@git.kernel.org>
Date:   Sat, 17 Feb 2018 02:13:02 -0800
From:   tip-bot for Borislav Petkov <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     arjan@...ux.intel.com, dan.j.williams@...el.com, mingo@...nel.org,
        luto@...nel.org, bp@...en8.de, gregkh@...uxfoundation.org,
        hpa@...or.com, dwmw2@...radead.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, ashok.raj@...el.com,
        dave.hansen@...ux.intel.com, bp@...e.de, peterz@...radead.org,
        jpoimboe@...hat.com, tglx@...utronix.de
Subject: [tip:x86/pti] x86/CPU: Check CPU feature bits after microcode
 upgrade

Commit-ID:  42ca8082e260dcfd8afa2afa6ec1940b9d41724c
Gitweb:     https://git.kernel.org/tip/42ca8082e260dcfd8afa2afa6ec1940b9d41724c
Author:     Borislav Petkov <bp@...e.de>
AuthorDate: Fri, 16 Feb 2018 12:26:40 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sat, 17 Feb 2018 08:43:55 +0100

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@...el.com>
Tested-by: Ashok Raj <ashok.raj@...el.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Ashok Raj <ashok.raj@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20180216112640.11554-4-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@...nel.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");
 }