x86/microcode: Rip out the subsys interface gunk

mainline inclusion
from mainline-v6.2-rc1
commit b6f86689
category: feature
feature: Backport Intel In Field Scan(IFS) multi-blob images support
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I6L337
CVE: N/A
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/


commit/?id=b6f86689

Intel-SIG: commit b6f86689 ("x86/microcode: Rip out the subsys interface gunk")

-------------------------------------

x86/microcode: Rip out the subsys interface gunk

This is a left-over from the old days when CPU hotplug wasn't as robust
as it is now. Currently, microcode gets loaded early on the CPU init
path and there's no need to attempt to load it again, which that subsys
interface callback is doing.

The only other thing that the subsys interface init path was doing is
adding the

  /sys/devices/system/cpu/cpu*/microcode/

hierarchy.

So add a function which gets called on each CPU after all the necessary
driver setup has happened. Use schedule_on_each_cpu() which can block
because the sysfs creating code does kmem_cache_zalloc() which can block
too and the initial version of this where it did that setup in an IPI
handler of on_each_cpu() can cause a deadlock of the sort:

  lock(fs_reclaim);
  <Interrupt>
    lock(fs_reclaim);

as the IPI handler runs in IRQ context.

Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Link: https://lore.kernel.org/r/20221028142638.28498-2-bp@alien8.de


Signed-off-by: Aichun Shi <aichun.shi@intel.com>