x86/CPU: Check CPU feature bits after microcode upgrade

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.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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 48d8fdd80b519f431bbb7c0ca0f445c0dc62db90..cf6380200dc29f897d1e6317d3445fda909ee95c 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1732,5 +1732,25 @@ 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");
 }