Hi, I have to clarify some things mentioned in my last post:
I only tested the change with an emulated EPYC-v2 CPU, I cannot test on a physical EPYC CPU at the moment. However, I doubt that the results will be different regarding the 0x8000_0008.ECX result. The topology information printed is from the EPYC-v2 CPU model. I try to get access to the machine and have a look if -cpu host affects this topology. So there is still the open question for the -enable-kvm -cpu host -smp 4 case. Shouldn't in this case the topology of the host CPU be reported? In all emulated-CPU cases it's on the user to define the topology or to live with the generated one (although I think preferring multi-socket systems is outdated, but it's likely just the case in my 'world'). Cheers, Philipp On 4/14/20 10:24 AM, Philipp Eppelt wrote: > Hi, > > thanks for looking into this so quickly. > > With this patch applied ontop of git commit > f3bac27cc1e303e1860cc55b9b6889ba39dee587 I still have the issue and it > reports the same numbers. I like the new usage of the ApicIdSize field. > > > I looked into the mentioned pc_smp_parse() and had it print the topology > for -smp 4: > > qemu-system-x86_64: warning: cpu topology: sockets (4) , dies (1) , > cores (1) , threads (1) , maxcpus (4), cpus (4) > > and with -smp 4,cores=4: > > qemu-system-x86_64: warning: cpu topology: sockets (1) , dies (1) , > cores (4) , threads (1) , maxcpus (4), cpus (4) > > As far as I understand it, these are the numbers the cpuid:8000'0008 > code relies on: > `cs->nr_cores`, `cs->nr_threads` with `cs` being of type CPUState. > > So I think the issue is rooted with the preferring sockets over cores > when the -smp cmdline option is parsed, as stated in hw/i386/pc.c:729. > > I guess this is the same code for Intel and AMD CPUs alike and this > issue just didn't surface for us on Intel CPUs, as they don't have this > CPUID leaf and we don't look at the topology. > > This seems to boil down to a more careful use of the -smp option on my end. > > Thanks again for looking into this. > > Cheers, > Philipp > > > > On 4/10/20 2:12 AM, Babu Moger wrote: >> Philipp, >> Can you please check if this patch works for you. >> >> diff --git a/target/i386/cpu.c b/target/i386/cpu.c >> index 90ffc5f..e467fee 100644 >> --- a/target/i386/cpu.c >> +++ b/target/i386/cpu.c >> @@ -5831,10 +5831,17 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t >> index, uint32_t count, >> } >> *ebx = env->features[FEAT_8000_0008_EBX]; >> *ecx = 0; >> - *edx = 0; >> if (cs->nr_cores * cs->nr_threads > 1) { >> - *ecx |= (cs->nr_cores * cs->nr_threads) - 1; >> + unsigned long max_apicids, bits_required; >> + >> + max_apicids = (cs->nr_cores * cs->nr_threads) - 1; >> + if (max_apicids) { >> + /* Find out the number of bits to represent all the >> apicids */ >> + bits_required = find_last_bit(&max_apicids, >> BITS_PER_BYTE) + 1; >> + *ecx |= bits_required << 12 | max_apicids; >> + } >> } >> + *edx = 0; >> break; >> case 0x8000000A: >> if (env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_SVM) { >> >> >> On 4/9/20 9:00 AM, Igor Mammedov wrote: >>> On Thu, 09 Apr 2020 12:58:11 -0000 >>> Philipp Eppelt <1871...@bugs.launchpad.net> wrote: >>> >>>> Public bug reported: >>>> >>>> Setup: >>>> CPU: AMD EPYC-v2 or host's EPYC cpu >>>> Linux 64-bit fedora host; Kernel version 5.5.15-200.fc31 >>>> qemu version: self build >>>> git-head: f3bac27cc1e303e1860cc55b9b6889ba39dee587 >>>> config: Configured with: '../configure' >>>> '--target-list=x86_64-softmmu,mips64el-softmmu,mips64-softmmu,mipsel-softmmu,mips-softmmu,i386-softmmu,aarch64-softmmu,arm-softmmu' >>>> '--prefix=/opt/qemu-master' >>>> >>>> Cmdline: >>>> qemu-system-x86_64 -kernel >>>> /home/peppelt/code/l4/internal/.build-x86_64/bin/amd64_gen/bootstrap >>>> -append "" -initrd "./fiasco/.build-x86_64/fiasco , ... " -serial stdio >>>> -nographic -monitor none -nographic -monitor none -cpu EPYC-v2 -m 4G -smp >>>> 4 >>>> >>>> Issue: >>>> We are developing an microkernel operating system called L4Re. We recently >>>> got an AMD EPYC server for testing and we couldn't execute SMP tests of >>>> our system when running Linux + qemu + VM w/ L4Re. >>>> In fact, the kernel did not recognize any APs at all. On AMD CPUs the >>>> kernel checks for the number of cores reported in CPUID leaf >>>> 0x8000_0008.ECX[NC] or [ApicIdSize]. [0][1] >>>> >>>> The physical machine reports for leaf 0x8000_0008: EAX: 0x3030 EBX: >>>> 0x18cf757 ECX: 0x703f EDX: 0x1000 >>>> The lower four bits of ECX are the [NC] field and all set. >>>> >>>> When querying inside qemu with -enable-kvm -cpu host -smp 4 (basically as >>>> replacement and addition to the above cmdline) the CPUID leaf shows: EAX: >>>> 0x3024, EBX: 0x1001000, ECX: 0x0, EDX: 0x0 >>>> Note, ECX is zero. Indicating that this is no SMP capabale CPU. >>>> >>>> I'm debugging it using my local machine and the QEMU provided EPYC-v2 >>>> CPU model and it is reproducible there as well and reports: EAX: >>>> 0x3028, EBX: 0x0, ECX: 0x0, EDX: 0x0 >>>> >>>> I checked other AMD based CPU models (phenom, opteron_g3/g5) and they >>>> behave the same. [2] shows the CPUID 0x8000'0008 handling in the QEMU >>>> source. >>>> I believe that behavior here is wrong as ECX[NC] should report the number >>>> of cores per processor, as stated in the AMD manual [2] p.584. In my >>>> understanding -smp 4 should then lead to ECX[NC] = 0x3. >>>> >>>> The following table shows my findings with the -smp option: >>>> Option | Qemu guest observed ECX value >>>> -smp 4 | 0x0 >>>> -smp 4,cores=4 | 0x3 >>>> -smp 4,cores=2,thread=2 | 0x3 >>>> -smp 4,cores=4,threads=2 | QEMU boot error: topology false. >>>> >>>> Now, I'm asking myself how the terminology of the AMD manual maps to >>>> QEMU's -smp option. >>>> Obviously, nr_cores and nr_threads correspond to the cores and threads >>>> options on the cmdline and cores * threads <= 4 (in this example), but >>>> what corresponds the X in -smp X to? >>> I'd say X corresponds to number of logical CPUs. >>> Depending on presence of other options these are distributed among them in >>> magical manner >>> (see pc_smp_parse() for starters) >>> >>>> Querying 0x8000'0008 on the physical processor results in different >>>> reports than quering QEMU's model as does it with -enable-kvm -cpu host. >>>> >>>> Furthermore, the ACPI.MADT shows 4 local APICs to be present while the >>>> CPU leave reports a single core processor. >>> it matches -smp X as it should be. >>> >>>> >>>> This leads me to the conclusion that CPUID 0x8000'0008.ECX reports the >>>> wrong number. >>> CCed author of recent epyc patches who might know how AMD should work >>> better than me. >>> >>>> >>>> Please let me know, if you need more information from my side. >>>> >>>> >>>> [0] >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fkernkonzept%2Ffiasco%2Fblob%2F522ccc5f29ab120213cf02d71328e2b879cbbd19%2Fsrc%2Fkern%2Fia32%2Fkernel_thread-ia32.cpp%23L109&data=02%7C01%7Cbabu.moger%40amd.com%7C57569f7959744399655b08d7dc8e6e24%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637220379083511672&sdata=hcFJzLAVQoIh5IN9CP%2F9cUQNOZoBnpRA6FliJur1wzQ%3D&reserved=0 >>>> [1] >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fkernkonzept%2Ffiasco%2Fblob%2F522ccc5f29ab120213cf02d71328e2b879cbbd19%2Fsrc%2Fkern%2Fia32%2Fcpu-ia32.cpp%23L1120&data=02%7C01%7Cbabu.moger%40amd.com%7C57569f7959744399655b08d7dc8e6e24%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637220379083511672&sdata=ANJIbYKbwfq2bDelH%2FRLKnDPIUZc1BwxHspmgxLU7gs%3D&reserved=0 >>>> [2] >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fqemu%2Fqemu%2Fblob%2Ff2a8261110c32c4dccd84e774d8dd7a0524e00fb%2Ftarget%2Fi386%2Fcpu.c%23L5835&data=02%7C01%7Cbabu.moger%40amd.com%7C57569f7959744399655b08d7dc8e6e24%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637220379083511672&sdata=oj3mv9e5YOzUsfUjXK44gC8LybyWgMKo8JBIrRR%2BmDA%3D&reserved=0 >>>> [3] >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.amd.com%2Fsystem%2Ffiles%2FTechDocs%2F24594.pdf&data=02%7C01%7Cbabu.moger%40amd.com%7C57569f7959744399655b08d7dc8e6e24%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637220379083511672&sdata=7Yr3J9ihlqSqXCXKN5JJNTByO3NGI%2BGMz2EqBF2Y4hw%3D&reserved=0 >>>> >>>> ** Affects: qemu >>>> Importance: Undecided >>>> Status: New >>>> >>> >> > -- philipp.epp...@kernkonzept.com - Tel. 0351-41 883 221 http://www.kernkonzept.com Kernkonzept GmbH. Sitz: Dresden. Amtsgericht Dresden, HRB 31129. Geschäftsführer: Dr.-Ing. Michael Hohmuth -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1871842 Title: AMD CPUID leaf 0x8000'0008 reported number of cores inconsistent with ACPI.MADT Status in QEMU: New Bug description: Setup: CPU: AMD EPYC-v2 or host's EPYC cpu Linux 64-bit fedora host; Kernel version 5.5.15-200.fc31 qemu version: self build git-head: f3bac27cc1e303e1860cc55b9b6889ba39dee587 config: Configured with: '../configure' '--target-list=x86_64-softmmu,mips64el-softmmu,mips64-softmmu,mipsel-softmmu,mips-softmmu,i386-softmmu,aarch64-softmmu,arm-softmmu' '--prefix=/opt/qemu-master' Cmdline: qemu-system-x86_64 -kernel /home/peppelt/code/l4/internal/.build-x86_64/bin/amd64_gen/bootstrap -append "" -initrd "./fiasco/.build-x86_64/fiasco , ... " -serial stdio -nographic -monitor none -nographic -monitor none -cpu EPYC-v2 -m 4G -smp 4 Issue: We are developing an microkernel operating system called L4Re. We recently got an AMD EPYC server for testing and we couldn't execute SMP tests of our system when running Linux + qemu + VM w/ L4Re. In fact, the kernel did not recognize any APs at all. On AMD CPUs the kernel checks for the number of cores reported in CPUID leaf 0x8000_0008.ECX[NC] or [ApicIdSize]. [0][1] The physical machine reports for leaf 0x8000_0008: EAX: 0x3030 EBX: 0x18cf757 ECX: 0x703f EDX: 0x1000 The lower four bits of ECX are the [NC] field and all set. When querying inside qemu with -enable-kvm -cpu host -smp 4 (basically as replacement and addition to the above cmdline) the CPUID leaf shows: EAX: 0x3024, EBX: 0x1001000, ECX: 0x0, EDX: 0x0 Note, ECX is zero. Indicating that this is no SMP capabale CPU. I'm debugging it using my local machine and the QEMU provided EPYC-v2 CPU model and it is reproducible there as well and reports: EAX: 0x3028, EBX: 0x0, ECX: 0x0, EDX: 0x0 I checked other AMD based CPU models (phenom, opteron_g3/g5) and they behave the same. [2] shows the CPUID 0x8000'0008 handling in the QEMU source. I believe that behavior here is wrong as ECX[NC] should report the number of cores per processor, as stated in the AMD manual [2] p.584. In my understanding -smp 4 should then lead to ECX[NC] = 0x3. The following table shows my findings with the -smp option: Option | Qemu guest observed ECX value -smp 4 | 0x0 -smp 4,cores=4 | 0x3 -smp 4,cores=2,thread=2 | 0x3 -smp 4,cores=4,threads=2 | QEMU boot error: topology false. Now, I'm asking myself how the terminology of the AMD manual maps to QEMU's -smp option. Obviously, nr_cores and nr_threads correspond to the cores and threads options on the cmdline and cores * threads <= 4 (in this example), but what corresponds the X in -smp X to? Querying 0x8000'0008 on the physical processor results in different reports than quering QEMU's model as does it with -enable-kvm -cpu host. Furthermore, the ACPI.MADT shows 4 local APICs to be present while the CPU leave reports a single core processor. This leads me to the conclusion that CPUID 0x8000'0008.ECX reports the wrong number. Please let me know, if you need more information from my side. [0] https://github.com/kernkonzept/fiasco/blob/522ccc5f29ab120213cf02d71328e2b879cbbd19/src/kern/ia32/kernel_thread-ia32.cpp#L109 [1] https://github.com/kernkonzept/fiasco/blob/522ccc5f29ab120213cf02d71328e2b879cbbd19/src/kern/ia32/cpu-ia32.cpp#L1120 [2] https://github.com/qemu/qemu/blob/f2a8261110c32c4dccd84e774d8dd7a0524e00fb/target/i386/cpu.c#L5835 [3] https://www.amd.com/system/files/TechDocs/24594.pdf To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1871842/+subscriptions