Support for parsing the topology on AMD/Hygon processors using CPUID leaf 0xb was added in commit 3986a0a805e6 ("x86/CPU/AMD: Derive CPU topology from CPUID function 0xB when available"). In an effort to keep all the topology parsing bits in one place, this commit also introduced a pseudo dependency on the TOPOEXT feature to parse the CPUID leaf 0xb.

TOPOEXT feature (CPUID 0x80000001 ECX[22]) advertises the support for Cache Properties leaf 0x8000001d and the CPUID leaf 0x8000001e EAX for "Extended APIC ID" however support for 0xb was introduced alongside the x2APIC support not only on AMD [1], but also historically on x86 [2].

Similar to 0xb, the support for extended CPU topology leaf 0x80000026 too does not depend on the TOPOEXT feature.

The support for these leaves is expected to be confirmed by ensuring "leaf <= {extended_}cpuid_level" and then parsing the level 0 of the respective leaf to confirm EBX[15:0] (LogProcAtThisLevel) is non-zero as stated in the definition of "CPUID_Fn0000000B_EAX_x00 [Extended Topology Enumeration] (Core::X86::Cpuid::ExtTopEnumEax0)" in Processor Programming Reference (PPR) for AMD Family 19h Model 01h Rev B1 Vol1 [3] Sec. 2.1.15.1 "CPUID Instruction Functions".

This has not been a problem on baremetal platforms since support for TOPOEXT (Fam 0x15 and later) predates the support for CPUID leaf 0xb (Fam 0x17[Zen2] and later), however, for AMD guests on QEMU, "x2apic" feature can be enabled independent of the "topoext" feature where QEMU expects topology and the initial APICID to be parsed using the CPUID leaf 0xb (especially when number of cores > 255) which is populated independent of the "topoext" feature flag.

Unconditionally call cpu_parse_topology_ext() on AMD and Hygon processors to first parse the topology using the XTOPOLOGY leaves (0x80000026 / 0xb) before using the TOPOEXT leaf (0x8000001e).

Cc: stable@vger.kernel.org # Only v6.9 and above Link: https://lore.kernel.org/lkml/1529686927-7665-1-git-send-email-suravee.suthik... [1] Link: https://lore.kernel.org/lkml/20080818181435.523309000@linux-os.sc.intel.com/ [2] Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 [3] Suggested-by: Naveen N Rao (AMD) naveen@kernel.org Fixes: 3986a0a805e6 ("x86/CPU/AMD: Derive CPU topology from CPUID function 0xB when available") Signed-off-by: K Prateek Nayak kprateek.nayak@amd.com --- Changelog v3..v4:

o Quoted relevant section of the PPR justifying the changes.

o Moved this patch up ahead.

o Cc'd stable and made a note that backports should target v6.9 and above since this depends on the x86 topology rewrite. --- arch/x86/kernel/cpu/topology_amd.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/topology_amd.c b/arch/x86/kernel/cpu/topology_amd.c index 827dd0dbb6e9..4e3134a5550c 100644 --- a/arch/x86/kernel/cpu/topology_amd.c +++ b/arch/x86/kernel/cpu/topology_amd.c @@ -175,18 +175,14 @@ static void topoext_fixup(struct topo_scan *tscan)

static void parse_topology_amd(struct topo_scan *tscan) { - bool has_topoext = false; - /* - * If the extended topology leaf 0x8000_001e is available - * try to get SMT, CORE, TILE, and DIE shifts from extended + * Try to get SMT, CORE, TILE, and DIE shifts from extended * CPUID leaf 0x8000_0026 on supported processors first. If * extended CPUID leaf 0x8000_0026 is not supported, try to * get SMT and CORE shift from leaf 0xb first, then try to * get the CORE shift from leaf 0x8000_0008. */ - if (cpu_feature_enabled(X86_FEATURE_TOPOEXT)) - has_topoext = cpu_parse_topology_ext(tscan); + bool has_topoext = cpu_parse_topology_ext(tscan);

if (cpu_feature_enabled(X86_FEATURE_AMD_HTR_CORES)) tscan->c->topo.cpu_type = cpuid_ebx(0x80000026);