[Xen-devel] [PATCH v4 0/4] CPUID-less CPU/sync_core fixes and improvements

[Andy Lutomirski <luto@xxxxxxxxxx>]

*** PATCHES 1 and 2 MAY BE 4.9 MATERIAL ***

Alan Cox pointed out that the 486 isn't the only supported CPU that
doesn't have CPUID.  Let's clean up the mess and make everything
faster while we're at it.

Patch 1 is intended to be an easy fix: it makes sync_core() work
without CPUID on all 32-bit kernels.  It should be quite safe.  This
will have a negligible performance cost during boot on kernels built
for newer CPUs.  With this in place, patch 2 reverts the buggy 486
check I added.

Patches 3-4 are meant to improve the situation.  Patch 3 cleans up
the Intel microcode loader and the patch 4 (which depends on patch 3
to work correctly) stops using CPUID in sync_core() altogether.

Changes from v3:
 - Improve sync_core() comments.
 - Tidy up sync_core() asm.

Changes from v2:
 - Switch to IRET-to-self and get rid of all the paravirt code.
 - Further immprove the sync_core() comment.

Changes from v1:
 - Fix Xen
 - Add timing info to the changelog (hint: 2x speedup)
 - Document patch 1 a bit better.

Andy Lutomirski (4):
  x86/asm/32: Make sync_core() handle missing CPUID on all 32-bit
    kernels
  Revert "x86/boot: Fail the boot if !M486 and CPUID is missing"
  x86/microcode/intel: Replace sync_core() with native_cpuid()
  x86/asm: Rewrite sync_core() to use IRET-to-self

 arch/x86/boot/cpu.c                   |  6 ---
 arch/x86/include/asm/processor.h      | 80 +++++++++++++++++++++++++----------
 arch/x86/kernel/cpu/microcode/intel.c | 26 ++++++++++--
 3 files changed, 81 insertions(+), 31 deletions(-)

-- 
2.9.3


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