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K Prateek Nayak c2415c407a x86/cpu/topology: Use initial APIC ID from XTOPOLOGY leaf on AMD/HYGON 
Prior to the topology parsing rewrite and the switchover to the new parsing
logic for AMD processors in

  c749ce393b ("x86/cpu: Use common topology code for AMD"),

the initial_apicid on these platforms was:

- First initialized to the LocalApicId from CPUID leaf 0x1 EBX[31:24].

- Then overwritten by the ExtendedLocalApicId in CPUID leaf 0xb
  EDX[31:0] on processors that supported topoext.

With the new parsing flow introduced in

  f7fb3b2dd9 ("x86/cpu: Provide an AMD/HYGON specific topology parser"),

parse_8000_001e() now unconditionally overwrites the initial_apicid already
parsed during cpu_parse_topology_ext().

Although this has not been a problem on baremetal platforms, on virtualized AMD
guests that feature more than 255 cores, QEMU zeros out the CPUID leaf
0x8000001e on CPUs with CoreID > 255 to prevent collision of these IDs in
EBX[7:0] which can only represent a maximum of 255 cores [1].

This results in the following FW_BUG being logged when booting a guest
with more than 255 cores:

    [Firmware Bug]: CPU 512: APIC ID mismatch. CPUID: 0x0000 APIC: 0x0200

AMD64 Architecture Programmer's Manual Volume 2: System Programming Pub.
24593 Rev. 3.42 [2] Section 16.12 "x2APIC_ID" mentions the Extended
Enumeration leaf 0xb (Fn0000_000B_EDX[31:0])(which was later superseded by the
extended leaf 0x80000026) provides the full x2APIC ID under all circumstances
unlike the one reported by CPUID leaf 0x8000001e EAX which depends on the mode
in which APIC is configured.

Rely on the APIC ID parsed during cpu_parse_topology_ext() from CPUID leaf
0x80000026 or 0xb and only use the APIC ID from leaf 0x8000001e if
cpu_parse_topology_ext() failed (has_topoext is false).

On platforms that support the 0xb leaf (Zen2 or later, AMD guests on
QEMU) or the extended leaf 0x80000026 (Zen4 or later), the
initial_apicid is now set to the value parsed from EDX[31:0].

On older AMD/Hygon platforms that do not support the 0xb leaf but support the
TOPOEXT extension (families 0x15, 0x16, 0x17[Zen1], and Hygon), retain current
behavior where the initial_apicid is set using the 0x8000001e leaf.

Issue debugged by Naveen N Rao (AMD) <naveen@kernel.org> and Sairaj Kodilkar
<sarunkod@amd.com>.

  [ bp: Massage commit message. ]

Fixes: c749ce393b ("x86/cpu: Use common topology code for AMD")
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Naveen N Rao (AMD) <naveen@kernel.org>
Cc: stable@vger.kernel.org
Link: https://github.com/qemu/qemu/commit/35ac5dfbcaa4b [1]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 [2]
Link: https://lore.kernel.org/20250825075732.10694-2-kprateek.nayak@amd.com
2025-08-27 11:31:11 +02:00
arch x86/cpu/topology: Use initial APIC ID from XTOPOLOGY leaf on AMD/HYGON 2025-08-27 11:31:11 +02:00
block block: avoid cpu_hotplug_lock depedency on freeze_lock 2025-08-21 07:11:11 -06:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto Significant patch series in this pull request: 2025-08-03 16:23:09 -07:00
Documentation Driver core fixes for 6.16-rc3 2025-08-23 09:04:32 -04:00
drivers i2c-for-6.17-rc3 2025-08-24 10:32:04 -04:00
fs Driver core fixes for 6.16-rc3 2025-08-23 09:04:32 -04:00
include USB fixes for 6.17-rc3 2025-08-23 11:21:56 -04:00
init Significant patch series in this pull request: 2025-08-03 16:23:09 -07:00
io_uring io_uring: clear ->async_data as part of normal init 2025-08-21 13:54:01 -06:00
ipc vfs-6.17-rc1.mmap_prepare 2025-07-28 13:43:25 -07:00
kernel - Fix a case where the events throttling logic operates on inactive events 2025-08-24 10:13:05 -04:00
lib Crypto library fixes for v6.17-rc3 2025-08-21 04:54:01 -07:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm Driver core fixes for 6.16-rc3 2025-08-23 09:04:32 -04:00
net netfilter: nf_reject: don't leak dst refcount for loopback packets 2025-08-21 10:02:00 -07:00
rust Driver core fixes for 6.16-rc3 2025-08-23 09:04:32 -04:00
samples Significant patch series in this pull request: 2025-08-03 16:23:09 -07:00
scripts Kbuild updates for v6.17 2025-08-06 07:32:52 +03:00
security + Features 2025-08-04 08:17:28 -07:00
sound ALSA: usb-audio: Use correct sub-type for UAC3 feature unit validation 2025-08-21 17:10:14 +02:00
tools tracing fixes for v6.17-rc2: 2025-08-23 10:11:34 -04:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt Merge tag 'kvm-x86-no_assignment-6.17' of https://github.com/kvm-x86/linux into HEAD 2025-07-29 08:36:42 -04:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore gitignore: allow .pylintrc to be tracked 2025-07-02 17:10:04 -06:00
.mailmap .mailmap: add entry for Easwar Hariharan 2025-08-19 16:35:55 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Kbuild updates for v6.17 2025-08-06 07:32:52 +03:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS i2c-for-6.17-rc3 2025-08-24 10:32:04 -04:00
Makefile Linux 6.17-rc3 2025-08-24 12:04:12 -04:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.