Linux Returns To Parallel CPU Microcode Updates To Reduce Cloud Disruption

[George99]

Ahhh, ok. Thanks for clarify this!

[nivedita]

It's even more surprising that a SMT capable core gets updated per SMT thread i.e. twice - as far as I understand what Michael wrote.

No, only one of the SMT siblings applies the update. What he said is that the patch ensures that the other ones don't try to do the update as well.

[waxhead]

I've never heard of "hotswap" x86 CPUs in the modern day, and I don't think you can have "offline" CPUs either. It can be idle and/or sleep, but it's not "offline" without going in the UEFI settings and disable the second (third, fourth, whatever) socket.

So I think all you said requires a reboot.

NUMA nodes (that has a CPU + memory + IO lanes) can be hot plugged.

To offline a CPU all you have to do is echo 0 (offline) or 1 (online) to a file in sysfs. So in case you want to offline CPU number 14 all you have to do is:
echo 0 > /sys/devices/system/cpu/cpu14/online
(and echo1 > ...) to online it again...

References...
https://www.youtube.com/watch?v=VE_P3ti2VWY (look at about 6:00, where some of the use cases are pointed out)
http://lkml.iu.edu/hypermail/linux/k...2.1/01135.html
https://www.kernel.org/doc/html/v4.1...u_hotplug.html

[starshipeleven]

Out of pure morbid curiosity does anyone know if microcode update are auto-applied if you do a CPU hotswap or fire up an offline CPU on a large system do you have to trigger that manually?

I've never heard of "hotswap" x86 CPUs in the modern day, and I don't think you can have "offline" CPUs either. It can be idle and/or sleep, but it's not "offline" without going in the UEFI settings and disable the second (third, fourth, whatever) socket.

So I think all you said requires a reboot.

[cl333r]

now i wonder what would happen if the kernel is hacked to load different versions of the firmware on each core/thread 😁😁

While you're updating a cloud of servers? Easy. Follow these 3 simple steps:

- Squat
- Bend down with your head between your legs
- Kiss your ass goodbye

[flower]

now i wonder what would happen if the kernel is hacked to load different versions of the firmware on each core/thread 😁😁

Maybe we can have specter hardened cores and fast ones xD
And all security related apps only runs in the firmer

[tajjada]

now i wonder what would happen if the kernel is hacked to load different versions of the firmware on each core/thread 😁😁

[George99]

I find it surprising that microcode updates is not per socket, but instead per core.

It's even more surprising that a SMT capable core gets updated per SMT thread i.e. twice - as far as I understand what Michael wrote.

[waxhead]

I find it surprising that microcode updates is not per socket, but instead per core. I know there exists CPUs that have other layouts where this does not make sense, but for "off the shelf" Intel CPUs the cores are usually the same per socket. Out of pure morbid curiosity does anyone know if microcode update are auto-applied if you do a CPU hotswap or fire up an offline CPU on a large system do you have to trigger that manually?

[bug77]

See? And you thought Intel was evil for keeping the core count low. They were only thinking of server downtimes :P