x86/microcode/intel: Check microcode revision before updating sibling threads

commit c182d2b7d0ca48e0d6ff16f7d883161238c447ed upstream.

After updating microcode on one of the threads of a core, the other
thread sibling automatically gets the update since the microcode
resources on a hyperthreaded core are shared between the two threads.

Check the microcode revision on the CPU before performing a microcode
update and thus save us the WRMSR 0x79 because it is a particularly
expensive operation.

[ Borislav: Massage changelog and coding style. ]

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Tested-by: Ashok Raj <ashok.raj@intel.com>
Cc: Arjan Van De Ven <arjan.van.de.ven@intel.com>
Link: http://lkml.kernel.org/r/1519352533-15992-2-git-send-email-ashok.raj@intel.com
Link: https://lkml.kernel.org/r/20180228102846.13447-3-bp@alien8.de
[bwh: Backported to 4.9: return 0 in this case]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index af8fc3b..8faa5fa 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -617,6 +617,17 @@ static int apply_microcode_early(struct ucode_cpu_info *uci, bool early)
        if (!mc)
                return 0;
 
+       /*
+        * Save us the MSR write below - which is a particular expensive
+        * operation - when the other hyperthread has updated the microcode
+        * already.
+        */
+       rev = intel_get_microcode_revision();
+       if (rev >= mc->hdr.rev) {
+               uci->cpu_sig.rev = rev;
+               return 0;
+       }
+
        /* write microcode via MSR 0x79 */
        native_wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);
 
@@ -891,7 +902,7 @@ static int apply_microcode_intel(int cpu)
 {
        struct microcode_intel *mc;
        struct ucode_cpu_info *uci;
-       struct cpuinfo_x86 *c;
+       struct cpuinfo_x86 *c = &cpu_data(cpu);
        static int prev_rev;
        u32 rev;
 
@@ -912,6 +923,18 @@ static int apply_microcode_intel(int cpu)
        if (!get_matching_mc(mc, cpu))
                return 0;
 
+       /*
+        * Save us the MSR write below - which is a particular expensive
+        * operation - when the other hyperthread has updated the microcode
+        * already.
+        */
+       rev = intel_get_microcode_revision();
+       if (rev >= mc->hdr.rev) {
+               uci->cpu_sig.rev = rev;
+               c->microcode = rev;
+               return 0;
+       }
+
        /* write microcode via MSR 0x79 */
        wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);
 
@@ -932,8 +955,6 @@ static int apply_microcode_intel(int cpu)
                prev_rev = rev;
        }
 
-       c = &cpu_data(cpu);
-
        uci->cpu_sig.rev = rev;
        c->microcode = rev;