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Then NB features like EDAC or GART IOMMU aren't available. >> >> Which was maybe not a bad idea, nobody expects those things to work >> on selected nodes only. (I think?) But it relies on the optimistic >> assumption that topology knows the true number of nodes. >> >> Today I tested 5 older AMD64 systems with socket 754/AM2+/AM3/AM3+ >> on MSI/ASUS motherboards. *All* of them report more than one node if >> the CPU has fewer cores than supported by the BIOS. >> >> (I also have one AM4 system which is OK, but can't speak for others). >> >> This is due to peculiarity of their MADT tables - they report as many >> LAPICs as the BIOS can support and excess LAPICs are simply disabled. >> FWIW, it's also a pattern that disabled APIC IDs have 0x80 bit set. >> >> The kernel counts this as "hotpluggable CPUs", since supposedly it's >> indistinguishable from actual multi-socket systems before ACPI 6.3, >> where the "online capable" flag was added to disambiguate hotplug and >> nonexistent but theoretically supported CPUs. >> >> Or at least that's what commit fed8d8773b8e ("x86/acpi/boot: Correct >> acpi_is_processor_usable() check") seems to imply. >> >> On pre-ACPI 6.3 systems those disabled LAPICs inflate topology size >> and result in breakage on recent kernels. A few examples below give >> an idea what those MADTs look like and how the kernel reads them. >> >> Regards, >> Michal >> >> >> Athlon 3000+ on S754: >> >> [02Fh 0047 001h] Local Apic ID : 00 >> [030h 0048 004h] Flags (decoded below) : 00000001 # enabled >> -- >> [037h 0055 001h] Local Apic ID : 81 >> [038h 0056 004h] Flags (decoded below) : 00000000 >> >> [ 0.027690] CPU topo: Max. logical packages: 2 >> [ 0.027691] CPU topo: Max. logical dies: 2 >> [ 0.027692] CPU topo: Max. dies per package: 1 >> [ 0.027703] CPU topo: Max. threads per core: 1 >> [ 0.027704] CPU topo: Num. cores per package: 1 >> [ 0.027705] CPU topo: Num. threads per package: 1 >> [ 0.027706] CPU topo: Allowing 1 present CPUs plus 1 hotplug CPUs >> >> Athlon II X2 250 on AM3+: >> >> [02Fh 0047 001h] Local Apic ID : 00 >> [030h 0048 004h] Flags (decoded below) : 00000001 # enabled >> -- >> [037h 0055 001h] Local Apic ID : 01 >> [038h 0056 004h] Flags (decoded below) : 00000001 # enabled >> -- >> [03Fh 0063 001h] Local Apic ID : 82 >> [040h 0064 004h] Flags (decoded below) : 00000000 >> -- >> [047h 0071 001h] Local Apic ID : 83 >> [048h 0072 004h] Flags (decoded below) : 00000000 >> -- >> [04Fh 0079 001h] Local Apic ID : 84 >> [050h 0080 004h] Flags (decoded below) : 00000000 >> -- >> [057h 0087 001h] Local Apic ID : 85 >> [058h 0088 004h] Flags (decoded below) : 00000000 >> -- >> [05Fh 0095 001h] Local Apic ID : 86 >> [060h 0096 004h] Flags (decoded below) : 00000000 >> -- >> [067h 0103 001h] Local Apic ID : 87 >> [068h 0104 004h] Flags (decoded below) : 00000000 >> >> [ 0.147372] CPU topo: Max. logical packages: 3 # not sure why not 4 >> [ 0.147372] CPU topo: Max. logical dies: 3 >> [ 0.147373] CPU topo: Max. dies per package: 1 >> [ 0.147379] CPU topo: Max. threads per core: 1 >> [ 0.147379] CPU topo: Num. cores per package: 2 >> [ 0.147380] CPU topo: Num. threads per package: 2 >> [ 0.147381] CPU topo: Allowing 2 present CPUs plus 6 hotplug CPUs >> >> Phenom II X4 965 on AM3: >> >> [02Fh 0047 1] Local Apic ID : 00 >> [030h 0048 4] Flags (decoded below) : 00000001 # enabled >> -- >> [037h 0055 1] Local Apic ID : 01 >> [038h 0056 4] Flags (decoded below) : 00000001 # enabled >> -- >> [03Fh 0063 1] Local Apic ID : 02 >> [040h 0064 4] Flags (decoded below) : 00000001 # enabled >> -- >> [047h 0071 1] Local Apic ID : 03 >> [048h 0072 4] Flags (decoded below) : 00000001 # enabled >> -- >> [04Fh 0079 1] Local Apic ID : 84 >> [050h 0080 4] Flags (decoded below) : 00000000 >> -- >> [057h 0087 1] Local Apic ID : 85 >> [058h 0088 4] Flags (decoded below) : 00000000 >> >> [ 0.072112] CPU topo: Max. logical packages: 2 >> [ 0.072112] CPU topo: Max. logical dies: 2 >> [ 0.072113] CPU topo: Max. dies per package: 1 >> [ 0.072118] CPU topo: Max. threads per core: 1 >> [ 0.072118] CPU topo: Num. cores per package: 4 >> [ 0.072119] CPU topo: Num. threads per package: 4 >> [ 0.072120] CPU topo: Allowing 4 present CPUs plus 2 hotplug CPUs > > So far, I think the way to go is add explicit quirk for known issues. > > Please see the patch below. > > Thanks, > Yazen > > > From eeb0745e973055d8840b536cfa842d6f2bf4ac52 Mon Sep 17 00:00:00 2001 > From: Yazen Ghannam > Date: Fri, 24 Oct 2025 21:19:26 +0000 > Subject: [PATCH] x86/topology: Add helper to ignore bogus MADT entries > > Some older Intel and AMD systems include bogus ACPI MADT entries. These > entries show as "disabled". And it's not clear if they are physically > present but offline, i.e halted. Or if they are not physically present > at all. > > Ideally, if they are not physically present, then they should not be > listed in MADT. There doesn't seem to be any explicit x86 topology info > that can be used to verify if the entries are bogus or not. > > Add a helper function to collect vendor-specific checks to ignore bogus > APIC IDs. Start with known quirks for an Intel SNB model and older AMD > K10 models. > > Fixes: f0551af02130 ("x86/topology: Ignore non-present APIC IDs in a present package") > Signed-off-by: Yazen Ghannam > --- > arch/x86/kernel/cpu/topology.c | 52 ++++++++++++++++++++++++++-------- > 1 file changed, 40 insertions(+), 12 deletions(-) > > diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c > index 6073a16628f9..704788b92395 100644 > --- a/arch/x86/kernel/cpu/topology.c > +++ b/arch/x86/kernel/cpu/topology.c > @@ -219,6 +219,45 @@ static unsigned int topo_unit_count(u32 lvlid, enum x86_topology_domains at_leve > return cnt; > } > > +/* > + * Some older BIOSes include extra entries in MADT. > + * Do some vendor-specific checks to ignore them. > + */ > +static bool ignore_extra_apic_entry(u32 apic_id) > +{ > + u32 pkgid = topo_apicid(apic_id, TOPO_PKG_DOMAIN); > + struct cpuinfo_x86 *c = &boot_cpu_data; > + > + /* Allow "physically not possible" cases if in a guest. */ > + if (!hypervisor_is_type(X86_HYPER_NATIVE)) > + return false; > + > + /* This model only supports 8 threads in a package. */ > + if (c->x86_vendor == X86_VENDOR_INTEL && > + c->x86 == 0x6 && c->x86_model == 0x2d) { > + if (topo_unit_count(pkgid, TOPO_PKG_DOMAIN, phys_cpu_present_map) >= 8) > + goto reject; > + } > + > + /* > + * Various older models have extra entries. A common trait is that the > + * package ID derived from the APIC ID would be more than was ever supported. > + */ > + if (c->x86_vendor == X86_VENDOR_AMD && c->x86 < 0x17) { Maybe look for lack of X86_FEATURE_ZEN instead? > + pkgid >>= x86_topo_system.dom_shifts[TOPO_PKG_DOMAIN - 1]; > + > + if (pkgid >= 8) > + goto reject; > + } > + > + return false; > + > +reject: > + pr_info_once("Ignoring hot-pluggable APIC ID %x.\n", apic_id); > + topo_info.nr_rejected_cpus++; > + return true; > +} > + > static __init void topo_register_apic(u32 apic_id, u32 acpi_id, bool present) > { > int cpu, dom; > @@ -240,19 +279,8 @@ static __init void topo_register_apic(u32 apic_id, u32 acpi_id, bool present) > cpuid_to_apicid[cpu] = apic_id; > topo_set_cpuids(cpu, apic_id, acpi_id); > } else { > - u32 pkgid = topo_apicid(apic_id, TOPO_PKG_DOMAIN); > - > - /* > - * Check for present APICs in the same package when running > - * on bare metal. Allow the bogosity in a guest. > - */ > - if (hypervisor_is_type(X86_HYPER_NATIVE) && > - topo_unit_count(pkgid, TOPO_PKG_DOMAIN, phys_cpu_present_map)) { > - pr_info_once("Ignoring hot-pluggable APIC ID %x in present package.\n", > - apic_id); > - topo_info.nr_rejected_cpus++; > + if (ignore_extra_apic_entry(apic_id)) > return; > - } > > topo_info.nr_disabled_cpus++; > }