4.15-stable review patch.  If anyone has any objections, please let me know.


From: Borislav Petkov <b...@suse.de>

commit 42ca8082e260dcfd8afa2afa6ec1940b9d41724c upstream.

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....@intel.com>
Tested-by: Ashok Raj <ashok....@intel.com>
Signed-off-by: Borislav Petkov <b...@suse.de>
Reviewed-by: Ashok Raj <ashok....@intel.com>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Arjan van de Ven <ar...@linux.intel.com>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Dan Williams <dan.j.willi...@intel.com>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: David Woodhouse <dw...@infradead.org>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Josh Poimboeuf <jpoim...@redhat.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Link: http://lkml.kernel.org/r/20180216112640.11554-4...@alien8.de
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

 arch/x86/kernel/cpu/common.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- 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;
+       /* 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, 
+       get_cpu_cap(&info);
+       if (!memcmp(&info.x86_capability, &boot_cpu_data.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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