[4.15 & 4.14 stable 05/12] x86/microcode/intel: Check microcode revision before updating sibling threads

From: Ashok Raj
Date: Fri Apr 06 2018 - 14:31:16 EST


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@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Tested-by: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Asit K Mallick <asit.k.mallick@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Arjan Van De Ven <arjan.van.de.ven@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1519352533-15992-2-git-send-email-ashok.raj@xxxxxxxxx
Link: https://lkml.kernel.org/r/20180228102846.13447-3-bp@xxxxxxxxx
---
arch/x86/kernel/cpu/microcode/intel.c | 27 ++++++++++++++++++++++++---
1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 923054a..87bd6dc 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -589,6 +589,17 @@ 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 UCODE_OK;
+ }
+
/* write microcode via MSR 0x79 */
native_wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);

@@ -776,7 +787,7 @@ static enum ucode_state 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;

@@ -793,6 +804,18 @@ static enum ucode_state apply_microcode_intel(int cpu)
return UCODE_NFOUND;
}

+ /*
+ * 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 UCODE_OK;
+ }
+
/* write microcode via MSR 0x79 */
wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);

@@ -813,8 +836,6 @@ static enum ucode_state apply_microcode_intel(int cpu)
prev_rev = rev;
}

- c = &cpu_data(cpu);
-
uci->cpu_sig.rev = rev;
c->microcode = rev;

--
2.7.4