The APIC ID is decoded based on the sequence sockets->dies->cores->threads. This works fine for most standard AMD and other vendors' configurations, but this decoding sequence does not follow that of AMD's APIC ID enumeration strictly. In some cases this can cause CPU topology inconsistency.
When booting a guest VM, the kernel tries to validate the topology, and finds it inconsistent with the enumeration of EPYC cpu models. The more details are in the bug https://bugzilla.redhat.com/show_bug.cgi?id=1728166. To fix the problem we need to build the topology as per the Processor Programming Reference (PPR) for AMD Family 17h Model 01h, Revision B1 Processors. The documentation is available from the bugzilla Link below. Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 It is also available at https://www.amd.com/system/files/TechDocs/55570-B1_PUB.zip Here is the text from the PPR. Operating systems are expected to use Core::X86::Cpuid::SizeId[ApicIdSize], the number of least significant bits in the Initial APIC ID that indicate core ID within a processor, in constructing per-core CPUID masks. Core::X86::Cpuid::SizeId[ApicIdSize] determines the maximum number of cores (MNC) that the processor could theoretically support, not the actual number of cores that are actually implemented or enabled on the processor, as indicated by Core::X86::Cpuid::SizeId[NC]. Each Core::X86::Apic::ApicId[ApicId] register is preset as follows: • ApicId[6] = Socket ID. • ApicId[5:4] = Node ID. • ApicId[3] = Logical CCX L3 complex ID • ApicId[2:0]= (SMT) ? {LogicalCoreID[1:0],ThreadId} : {1'b0,LogicalCoreID[1:0]} The new apic id encoding is enabled for EPYC and EPYC-Rome models. Signed-off-by: Babu Moger <babu.mo...@amd.com> Acked-by: Michael S. Tsirkin <m...@redhat.com> Acked-by: Igor Mammedov <imamm...@redhat.com> --- target/i386/cpu.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/target/i386/cpu.c b/target/i386/cpu.c index 1e4400df7a..9ffaf5e2a0 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -3925,6 +3925,7 @@ static X86CPUDefinition builtin_x86_defs[] = { .xlevel = 0x8000001E, .model_id = "AMD EPYC Processor", .cache_info = &epyc_cache_info, + .use_epyc_apic_id_encoding = 1, .versions = (X86CPUVersionDefinition[]) { { .version = 1 }, { @@ -4052,6 +4053,7 @@ static X86CPUDefinition builtin_x86_defs[] = { .xlevel = 0x8000001E, .model_id = "AMD EPYC-Rome Processor", .cache_info = &epyc_rome_cache_info, + .use_epyc_apic_id_encoding = 1, }, };
