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Subject[PATCH] Parallel microcode update in Linux
Date
This patch enables parallel microcode loading. In order to measure the
improvements of parallel vs serial, we have used the following diff:

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 577b223..1ea08d8 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -614,17 +614,25 @@ static int __reload_late(void *info)
*/
static int microcode_reload_late(void)
{
+ u64 p0, p1;
int ret;

atomic_set(&late_cpus_in, 0);
atomic_set(&late_cpus_out, 0);

+ p0 = rdtsc_ordered();
+
ret = stop_machine_cpuslocked(__reload_late, NULL, cpu_online_mask);
+
+ p1 = rdtsc_ordered();
+
if (ret > 0)
microcode_check();

pr_info("Reload completed, microcode revision: 0x%x\n", boot_cpu_data.microcode);

+ pr_info("p0: %lld, p1: %lld, diff: %lld\n", p0, p1, p1 - p0);
+
return ret;
}

We have used a machine with a broken microcode in BIOS and no microcode in
initramfs (to bypass early loading).
Here are the results for parallel loading (we made two measurements):

[root@ovs108 ~]# uname -a
Linux ovs108 5.3.0-rc5.master.parallel.el7.dev.x86_64 #1 SMP Thu Aug 22 10:17:04 GMT 2019 x86_64 x86_64 x86_64 GNU/Linux
[root@ovs108 ~]# dmesg | grep microcode
[ 0.000000] Intel Spectre v2 broken microcode detected; disabling Speculation Control
[ 0.197658] MDS: Vulnerable: Clear CPU buffers attempted, no microcode
[ 2.114135] microcode: sig=0x50654, pf=0x80, revision=0x200003a
[ 2.117555] microcode: Microcode Update Driver: v2.2.
[ 18.197760] microcode: updated to revision 0x200005e, date = 2019-04-02
[ 18.201225] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
[ 18.201230] microcode: Reload completed, microcode revision: 0x200005e
[ 18.201232] microcode: p0: 118138123843052, p1: 118138153732656, diff: 29889604

[root@ovs108 ~]# dmesg | grep microcode
[ 0.000000] Intel Spectre v2 broken microcode detected; disabling Speculation Control
[ 0.195218] MDS: Vulnerable: Clear CPU buffers attempted, no microcode
[ 2.111882] microcode: sig=0x50654, pf=0x80, revision=0x200003a
[ 2.115265] microcode: Microcode Update Driver: v2.2.
[ 18.033397] microcode: updated to revision 0x200005e, date = 2019-04-02
[ 18.036590] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
[ 18.036595] microcode: Reload completed, microcode revision: 0x200005e
[ 18.036597] microcode: p0: 118947162428414, p1: 118947191490162, diff: 29061748
Here are the results of serial loading:

[root@ovs108 ~]# uname -a
Linux ovs108 5.3.0-rc5.master.serial.el7.dev.x86_64 #1 SMP Thu Aug 22 12:22:18 GMT 2019 x86_64 x86_64 x86_64 GNU/Linux
[root@ovs108 ~]# dmesg | grep microcode
[ 0.000000] Intel Spectre v2 broken microcode detected; disabling Speculation Control
[ 0.195158] MDS: Vulnerable: Clear CPU buffers attempted, no microcode
[ 2.111353] microcode: sig=0x50654, pf=0x80, revision=0x200003a
[ 2.114834] microcode: Microcode Update Driver: v2.2.
[ 17.542518] microcode: updated to revision 0x200005e, date = 2019-04-02
[ 17.898365] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
[ 17.898370] microcode: Reload completed, microcode revision: 0x200005e
[ 17.898372] microcode: p0: 149220216047388, p1: 149221058945422, diff: 842898034
[root@ovs108 ~]# dmesg | grep microcode
[ 0.000000] Intel Spectre v2 broken microcode detected; disabling Speculation Control
[ 0.197158] MDS: Vulnerable: Clear CPU buffers attempted, no microcode
[ 2.114005] microcode: sig=0x50654, pf=0x80, revision=0x200003a
[ 2.117451] microcode: Microcode Update Driver: v2.2.
[ 17.732026] microcode: updated to revision 0x200005e, date = 2019-04-02
[ 18.041398] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
[ 18.041404] microcode: Reload completed, microcode revision: 0x200005e
[ 18.041407] microcode: p0: 149835792698162, p1: 149836532930286, diff: 740232124

One can see that the difference is an order magnitude.

---
I also tested microcode loading with cpu hotplug.
- I unplugged the last two CPUs (basically the last core with 2 hyperthreads)
[ 1077.756759] IRQ 324: no longer affine to CPU71
[ 1077.756889] IRQ 619: no longer affine to CPU71
[ 1077.756908] IRQ 645: no longer affine to CPU71
[ 1077.761213] smpboot: CPU 71 is now offline
[ 1082.702759] IRQ 289: no longer affine to CPU70
[ 1082.702771] IRQ 305: no longer affine to CPU70
[ 1082.702827] IRQ 521: no longer affine to CPU70
[ 1082.702860] IRQ 636: no longer affine to CPU70
[ 1082.702876] IRQ 679: no longer affine to CPU70
[ 1082.706897] smpboot: CPU 70 is now offline

- I did the microcode update:
[ 1123.818741] microcode: updated to revision 0x200005e, date = 2019-04-02
[ 1123.821013] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
[ 1123.821014] x86/CPU: Please consider either early loading through initrd/built-in or a potential BIOS update.
[ 1123.821014] microcode: Reload completed, microcode revision: 0x200005e
[ 1123.821015] microcode: p0: 197460831869308, p1: 197460853607904, diff: 21738596
- Than I onlined CPU 70/71
[ 1151.170814] smpboot: Booting Node 1 Processor 70 APIC 0x75
[ 1151.177199] microcode: sig=0x50654, pf=0x80, revision=0x200005e
[ 1182.523811] smpboot: Booting Node 1 Processor 71 APIC 0x77
root@ovs108 ~]# cat /proc/cpuinfo | tr "\t" " " | grep -A 6 "processor : 70" | grep microcode
microcode : 0x200005e
[root@ovs108 ~]# cat /proc/cpuinfo | tr "\t" " " | grep -A 6 "processor : 71" | grep microcode
microcode : 0x200005e

We can see that both CPUs have been updated to the same microcode revision.

Thank you,
Mihai

Ashok Raj (1):
x86/microcode: Update microcode for all cores in parallel

arch/x86/kernel/cpu/microcode/core.c | 44 ++++++++++++++++++++++++-----------
arch/x86/kernel/cpu/microcode/intel.c | 14 ++++-------
2 files changed, 36 insertions(+), 22 deletions(-)
--
1.8.3.1

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