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[Xen-devel] [PATCH v4 0/6] improve late microcode loading

The intention of this series is to make the late microcode loading
more reliable by rendezvousing all cpus in stop_machine context and
updating microcode of each cpu core one-by-one. This idea comes from
Ashok. I am porting his linux patch to Xen (see patch 6 for more

This series makes two changes:
 1. Patch 1-5: introduce a global microcode cache
 2. Patch 6: synchronize late microcode loading

Currently, late microcode loading does a lot of things including
parsing microcode file, checking the signature/revision and performing
update. Putting all of them into stop_machine context is a bad idea
because of complexity (One issue I observed is memory allocation
triggered one assertion in stop_machine context). In order to simplify
the load process, I move parsing microcode out of the load process.
The microcode file is parsed and a global microcode cache is built on
a single CPU before rendezvousing all cpus to update microcode. Other
CPUs just get a suitable microcode from the global cache and load it.
With this global cache, it is safe to put simplified load process to
stop_machine context.

Regarding changes to AMD side, I didn't do any tests for them due to
lack of hardware. Hence it wonldn't be surprising to me if you found
some bugs on a AMD machine. Is there anyone who has a AMD machine
at hand willing to do some basic tests, like
* do a microcode update
* don't bring all pCPUs up at startup by specifying maxcpus in xen
  command line and then do a microcode update and online all
  offlined CPUs via 'xen-hptool'.

For your convenience, you can also find this series at:

Chao Gao (6):
  microcode/intel: extend microcode_update_match()
  microcode: save all microcodes which pass sanity check
  microcode: delete 'mc' field from struct ucode_cpu_info
  microcode: don't call apply_microcode() in cpu_request_microcode()
  microcode: delete microcode pointer and size from microcode_info
  x86/microcode: Synchronize late microcode loading

 xen/arch/x86/microcode.c        | 215 ++++++++++++++++++++++++++--------------
 xen/arch/x86/microcode_amd.c    | 183 ++++++++++++++++++----------------
 xen/arch/x86/microcode_intel.c  | 174 ++++++++++++++++++++++----------
 xen/include/asm-x86/microcode.h |  17 ++--
 4 files changed, 371 insertions(+), 218 deletions(-)


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