Any feedback or concerns with this patch? Otherwise can this be merged? Thanks Babu On 1/2/24 17:17, Babu Moger wrote: > Observed the following failure while booting the SEV-SNP guest and the > guest fails to boot with the smp parameters: > "-smp 192,sockets=1,dies=12,cores=8,threads=2". > > qemu-system-x86_64: sev_snp_launch_update: SNP_LAUNCH_UPDATE ret=-5 fw_error=22 'Invalid parameter' > qemu-system-x86_64: SEV-SNP: CPUID validation failed for function 0x8000001e, index: 0x0. > provided: eax:0x00000000, ebx: 0x00000100, ecx: 0x00000b00, edx: 0x00000000 > expected: eax:0x00000000, ebx: 0x00000100, ecx: 0x00000300, edx: 0x00000000 > qemu-system-x86_64: SEV-SNP: failed update CPUID page > > Reason for the failure is due to overflowing of bits used for "Node per > processor" in CPUID Fn8000001E_ECX. This field's width is 3 bits wide and > can hold maximum value 0x7. With dies=12 (0xB), it overflows and spills > over into the reserved bits. In the case of SEV-SNP, this causes CPUID > enforcement failure and guest fails to boot. > > The PPR documentation for CPUID_Fn8000001E_ECX [Node Identifiers] > ================================================================= > Bits Description > 31:11 Reserved. > > 10:8 NodesPerProcessor: Node per processor. Read-only. > ValidValues: > Value Description > 0h 1 node per processor. > 7h-1h Reserved. > > 7:0 NodeId: Node ID. Read-only. Reset: Fixed,XXh. > ================================================================= > > As in the spec, the valid value for "node per processor" is 0 and rest > are reserved. > > Looking back at the history of decoding of CPUID_Fn8000001E_ECX, noticed > that there were cases where "node per processor" can be more than 1. It > is valid only for pre-F17h (pre-EPYC) architectures. For EPYC or later > CPUs, the linux kernel does not use this information to build the L3 > topology. > > Also noted that the CPUID Function 0x8000001E_ECX is available only when > TOPOEXT feature is enabled. This feature is enabled only for EPYC(F17h) > or later processors. So, previous generation of processors do not not > enumerate 0x8000001E_ECX leaf. > > There could be some corner cases where the older guests could enable the > TOPOEXT feature by running with -cpu host, in which case legacy guests > might notice the topology change. To address those cases introduced a > new CPU property "legacy-multi-node". It will be true for older machine > types to maintain compatibility. By default, it will be false, so new > decoding will be used going forward. > > The documentation is taken from Preliminary Processor Programming > Reference (PPR) for AMD Family 19h Model 11h, Revision B1 Processors 55901 > Rev 0.25 - Oct 6, 2022. > > Cc: qemu-stable@xxxxxxxxxx > Fixes: 31ada106d891 ("Simplify CPUID_8000_001E for AMD") > Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 > Signed-off-by: Babu Moger <babu.moger@xxxxxxx> > Reviewed-by: Zhao Liu <zhao1.liu@xxxxxxxxx> > --- > v2: Rebased to the latest tree. > Updated the pc_compat_8_2 for the new flag. > Added the comment for new property legacy_multi_node. > Added Reviwed-by from Zhao. > --- > hw/i386/pc.c | 4 +++- > target/i386/cpu.c | 18 ++++++++++-------- > target/i386/cpu.h | 6 ++++++ > 3 files changed, 19 insertions(+), 9 deletions(-) > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index 496498df3a..a504e05e62 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -78,7 +78,9 @@ > { "qemu64-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, },\ > { "athlon-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, }, > > -GlobalProperty pc_compat_8_2[] = {}; > +GlobalProperty pc_compat_8_2[] = { > + { TYPE_X86_CPU, "legacy-multi-node", "on" }, > +}; > const size_t pc_compat_8_2_len = G_N_ELEMENTS(pc_compat_8_2); > > GlobalProperty pc_compat_8_1[] = {}; > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > index 95d5f16cd5..2cc84e8500 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -398,12 +398,9 @@ static void encode_topo_cpuid8000001e(X86CPU *cpu, X86CPUTopoInfo *topo_info, > * 31:11 Reserved. > * 10:8 NodesPerProcessor: Node per processor. Read-only. Reset: XXXb. > * ValidValues: > - * Value Description > - * 000b 1 node per processor. > - * 001b 2 nodes per processor. > - * 010b Reserved. > - * 011b 4 nodes per processor. > - * 111b-100b Reserved. > + * Value Description > + * 0h 1 node per processor. > + * 7h-1h Reserved. > * 7:0 NodeId: Node ID. Read-only. Reset: XXh. > * > * NOTE: Hardware reserves 3 bits for number of nodes per processor. > @@ -412,8 +409,12 @@ static void encode_topo_cpuid8000001e(X86CPU *cpu, X86CPUTopoInfo *topo_info, > * NodeId is combination of node and socket_id which is already decoded > * in apic_id. Just use it by shifting. > */ > - *ecx = ((topo_info->dies_per_pkg - 1) << 8) | > - ((cpu->apic_id >> apicid_die_offset(topo_info)) & 0xFF); > + if (cpu->legacy_multi_node) { > + *ecx = ((topo_info->dies_per_pkg - 1) << 8) | > + ((cpu->apic_id >> apicid_die_offset(topo_info)) & 0xFF); > + } else { > + *ecx = (cpu->apic_id >> apicid_pkg_offset(topo_info)) & 0xFF; > + } > > *edx = 0; > } > @@ -7895,6 +7896,7 @@ static Property x86_cpu_properties[] = { > * own cache information (see x86_cpu_load_def()). > */ > DEFINE_PROP_BOOL("legacy-cache", X86CPU, legacy_cache, true), > + DEFINE_PROP_BOOL("legacy-multi-node", X86CPU, legacy_multi_node, false), > DEFINE_PROP_BOOL("xen-vapic", X86CPU, xen_vapic, false), > > /* > diff --git a/target/i386/cpu.h b/target/i386/cpu.h > index ef987f344c..6ef4396fc5 100644 > --- a/target/i386/cpu.h > +++ b/target/i386/cpu.h > @@ -1989,6 +1989,12 @@ struct ArchCPU { > */ > bool legacy_cache; > > + /* Compatibility bits for old machine types. > + * If true decode the CPUID Function 0x8000001E_ECX to support multiple > + * nodes per processor > + */ > + bool legacy_multi_node; > + > /* Compatibility bits for old machine types: */ > bool enable_cpuid_0xb; > -- Thanks Babu Moger