The current implementation has a couple of shortcomings:
- It fails to handle hybrid systems correctly.
- The APIC registration code which handles CPU number assignents is in
the middle of the APIC code and detached from the topology evaluation.
- The various mechanisms which enumerate APICs, ACPI, MPPARSE and guest
specific ones, tweak global variables as they see fit or in case of
XENPV just hack around the generic mechanisms completely.
- The CPUID topology evaluation code is sprinkled all over the vendor
code and reevaluates global variables on every hotplug operation.
- There is no way to analyze topology on the boot CPU before bringing up
the APs. This causes problems for infrastructure like PERF which needs
to size certain aspects upfront or could be simplified if that would be
possible.
- The APIC admission and CPU number association logic is incomprehensible
and overly complex and needs to be kept around after boot instead of
completing this right after the APIC enumeration.
This update addresses these shortcomings with the following changes:
- Rework the CPUID evaluation code so it is common for all vendors and
provides information about the APIC ID segments in a uniform way
independent of the number of segments (Thread, Core, Module, ..., Die,
Package) so that this information can be computed instead of rewriting
global variables of dubious value over and over.
- A few cleanups and simplifcations of the APIC, IO/APIC and related
interfaces to prepare for the topology evaluation changes.
- Seperation of the parser stages so the early evaluation which tries to
find the APIC address can be seperately overridden from the late
evaluation which enumerates and registers the local APIC as further
preparation for sanitizing the topology evaluation.
- A new registration and admission logic which
- encapsulates the inner workings so that parsers and guest logic
cannot longer fiddle in it
- uses the APIC ID segments to build topology bitmaps at registration
time
- provides a sane admission logic
- allows to detect the crash kernel case, where CPU0 does not run on
the real BSP, automatically. This is required to prevent sending
INIT/SIPI sequences to the real BSP which would reset the whole
machine. This was so far handled by a tedious command line
parameter, which does not even work in nested crash scenarios.
- Associates CPU number after the enumeration completed and prevents
the late registration of APICs, which was somehow tolerated before.
- Converting all parsers and guest enumeration mechanisms over to the
new interfaces.
This allows to get rid of all global variable tweaking from the parsers
and enumeration mechanisms and sanitizes the XEN[PV] handling so it can
use CPUID evaluation for the first time.
- Mopping up existing sins by taking the information from the APIC ID
segment bitmaps.
This evaluates hybrid systems correctly on the boot CPU and allows for
cleanups and fixes in the related drivers, e.g. PERF.
The series has been extensively tested and the minimal late fallout due to
a broken ACPI/MADT table has been addressed by tightening the admission
logic further.
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Merge tag 'x86-apic-2024-03-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 APIC updates from Thomas Gleixner:
"Rework of APIC enumeration and topology evaluation.
The current implementation has a couple of shortcomings:
- It fails to handle hybrid systems correctly.
- The APIC registration code which handles CPU number assignents is
in the middle of the APIC code and detached from the topology
evaluation.
- The various mechanisms which enumerate APICs, ACPI, MPPARSE and
guest specific ones, tweak global variables as they see fit or in
case of XENPV just hack around the generic mechanisms completely.
- The CPUID topology evaluation code is sprinkled all over the vendor
code and reevaluates global variables on every hotplug operation.
- There is no way to analyze topology on the boot CPU before bringing
up the APs. This causes problems for infrastructure like PERF which
needs to size certain aspects upfront or could be simplified if
that would be possible.
- The APIC admission and CPU number association logic is
incomprehensible and overly complex and needs to be kept around
after boot instead of completing this right after the APIC
enumeration.
This update addresses these shortcomings with the following changes:
- Rework the CPUID evaluation code so it is common for all vendors
and provides information about the APIC ID segments in a uniform
way independent of the number of segments (Thread, Core, Module,
..., Die, Package) so that this information can be computed instead
of rewriting global variables of dubious value over and over.
- A few cleanups and simplifcations of the APIC, IO/APIC and related
interfaces to prepare for the topology evaluation changes.
- Seperation of the parser stages so the early evaluation which tries
to find the APIC address can be seperately overridden from the late
evaluation which enumerates and registers the local APIC as further
preparation for sanitizing the topology evaluation.
- A new registration and admission logic which
- encapsulates the inner workings so that parsers and guest logic
cannot longer fiddle in it
- uses the APIC ID segments to build topology bitmaps at
registration time
- provides a sane admission logic
- allows to detect the crash kernel case, where CPU0 does not run
on the real BSP, automatically. This is required to prevent
sending INIT/SIPI sequences to the real BSP which would reset
the whole machine. This was so far handled by a tedious command
line parameter, which does not even work in nested crash
scenarios.
- Associates CPU number after the enumeration completed and
prevents the late registration of APICs, which was somehow
tolerated before.
- Converting all parsers and guest enumeration mechanisms over to the
new interfaces.
This allows to get rid of all global variable tweaking from the
parsers and enumeration mechanisms and sanitizes the XEN[PV]
handling so it can use CPUID evaluation for the first time.
- Mopping up existing sins by taking the information from the APIC ID
segment bitmaps.
This evaluates hybrid systems correctly on the boot CPU and allows
for cleanups and fixes in the related drivers, e.g. PERF.
The series has been extensively tested and the minimal late fallout
due to a broken ACPI/MADT table has been addressed by tightening the
admission logic further"
* tag 'x86-apic-2024-03-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (76 commits)
x86/topology: Ignore non-present APIC IDs in a present package
x86/apic: Build the x86 topology enumeration functions on UP APIC builds too
smp: Provide 'setup_max_cpus' definition on UP too
smp: Avoid 'setup_max_cpus' namespace collision/shadowing
x86/bugs: Use fixed addressing for VERW operand
x86/cpu/topology: Get rid of cpuinfo::x86_max_cores
x86/cpu/topology: Provide __num_[cores|threads]_per_package
x86/cpu/topology: Rename topology_max_die_per_package()
x86/cpu/topology: Rename smp_num_siblings
x86/cpu/topology: Retrieve cores per package from topology bitmaps
x86/cpu/topology: Use topology logical mapping mechanism
x86/cpu/topology: Provide logical pkg/die mapping
x86/cpu/topology: Simplify cpu_mark_primary_thread()
x86/cpu/topology: Mop up primary thread mask handling
x86/cpu/topology: Use topology bitmaps for sizing
x86/cpu/topology: Let XEN/PV use topology from CPUID/MADT
x86/xen/smp_pv: Count number of vCPUs early
x86/cpu/topology: Assign hotpluggable CPUIDs during init
x86/cpu/topology: Reject unknown APIC IDs on ACPI hotplug
x86/topology: Add a mechanism to track topology via APIC IDs
...
