| From | Thomas Gleixner <> | Subject | [patch V4 00/30] x86/microcode: Cleanup and late loading enhancements | Date | Mon, 2 Oct 2023 13:59:34 +0200 (CEST) |
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This is a follow up on:
https://lore.kernel.org/lkml/20230912065249.695681286@linutronix.de
Late microcode loading is desired by enterprise users. Late loading is problematic as it requires detailed knowledge about the change and an analysis whether this change modifies something which is already in use by the kernel. Large enterprise customers have engineering teams and access to deep technical vendor support. The regular admin does not have such resources, so the kernel has always tainted the kernel after late loading.
Intel recently added a new previously reserved field to the microcode header which contains the minimal microcode revision which must be running on the CPU to make the load safe. This field is 0 in all older microcode revisions, which the kernel assumes to be unsafe. Minimal revision checking can be enforced via Kconfig or kernel command line. It then refuses to load an unsafe revision. The default loads unsafe revisions like before and taints the kernel. If a safe revision is loaded the kernel is not tainted.
But that does not solve all other known problems with late loading:
- Late loading on current Intel CPUs is unsafe vs. NMI when hyperthreading is enabled. If a NMI hits the secondary sibling while the primary loads the microcode, the machine can crash.
- Soft offline SMT siblings which are playing dead with MWAIT can cause damage too when the microcode update modifies MWAIT. That's a realistic scenario in the context of 'nosmt' mitigations. :(
Neither the core code nor the Intel specific code handles any of this at all.
While trying to implement this, I stumbled over disfunctional, horribly complex and redundant code, which I decided to clean up first so the new functionality can be added on a clean slate.
So the series has several sections:
1) Move the 32bit early loading after paging enable
2) Cleanup of the Intel specific code
3) Implementation of proper core control logic to handle the NMI safe requirements
4) Support for minimal revision check in the core and the Intel specific parts.
Changes vs. V3:
- Rebased on v6.6-rc1
- Remove the early load magic which was required for physical address mode from the AMD code.
- Address the review comments from Borislav, which is mostly naming, comments and change logs. No functional changes vs. v3
The series is also available from git:
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git ucode-v4
Thanks,
tglx --- Documentation/admin-guide/kernel-parameters.txt | 5 arch/x86/Kconfig | 25 arch/x86/include/asm/apic.h | 5 arch/x86/include/asm/cpu.h | 20 arch/x86/include/asm/microcode.h | 19 arch/x86/kernel/Makefile | 1 arch/x86/kernel/apic/apic_flat_64.c | 2 arch/x86/kernel/apic/ipi.c | 8 arch/x86/kernel/apic/x2apic_cluster.c | 1 arch/x86/kernel/apic/x2apic_phys.c | 1 arch/x86/kernel/cpu/common.c | 12 arch/x86/kernel/cpu/microcode/amd.c | 129 +--- arch/x86/kernel/cpu/microcode/core.c | 637 ++++++++++++++-------- arch/x86/kernel/cpu/microcode/intel.c | 682 +++++++----------------- arch/x86/kernel/cpu/microcode/internal.h | 32 - arch/x86/kernel/head32.c | 6 arch/x86/kernel/head_32.S | 10 arch/x86/kernel/nmi.c | 9 arch/x86/kernel/smpboot.c | 12 drivers/platform/x86/intel/ifs/load.c | 8 include/linux/cpuhotplug.h | 1 21 files changed, 788 insertions(+), 837 deletions(-)
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