linux-kernel - [PATCH v2 0/6] CPUID-less CPU/sync

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Date:   Thu,  1 Dec 2016 16:34:56 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        Borislav Petkov <bp@...en8.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Matthew Whitehead <tedheadster@...il.com>,
        Henrique de Moraes Holschuh <hmh@....eng.br>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2 0/6] CPUID-less CPU/sync_core fixes and improvements

*** 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 3-6 are meant to improve the situation.  Patch 3 cleans
up the Intel microcode loader and the rest (which depend on patch 3)
stops using CPUID in sync_core() altogether.

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

Andy Lutomirski (6):
  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 cpuid_eax(1)
  x86/paravirt: Make sync_core() be a paravirt op
  x86/xen: Add a Xen-specific sync_core() implementation
  x86/asm: Change sync_core() to use MOV to CR2 to serialize

 arch/x86/boot/cpu.c                   |  6 ------
 arch/x86/include/asm/paravirt.h       |  5 +++++
 arch/x86/include/asm/paravirt_types.h |  2 ++
 arch/x86/include/asm/processor.h      | 34 ++++++++++------------------------
 arch/x86/kernel/cpu/microcode/intel.c |  6 +++---
 arch/x86/kernel/paravirt.c            |  2 ++
 arch/x86/xen/enlighten.c              | 35 +++++++++++++++++++++++++++++++++++
 7 files changed, 57 insertions(+), 33 deletions(-)

-- 
2.9.3