On Thu, Jun 04, 2020 at 09:06:27AM -0500, Babu Moger wrote: > > > > -----Original Message----- > > From: Eduardo Habkost <ehabkost@xxxxxxxxxx> > > Sent: Tuesday, June 2, 2020 12:52 PM > > To: Moger, Babu <Babu.Moger@xxxxxxx> > > Cc: mst@xxxxxxxxxx; marcel.apfelbaum@xxxxxxxxx; pbonzini@xxxxxxxxxx; > > rth@xxxxxxxxxxx; mtosatti@xxxxxxxxxx; qemu-devel@xxxxxxxxxx; > > kvm@xxxxxxxxxxxxxxx; kash@xxxxxxxxxxxxxx; geoff@xxxxxxxxxxxxxxx; Dr. David > > Alan Gilbert <dgilbert@xxxxxxxxxx> > > Subject: Re: [PATCH v13 1/5] i386: Add support for CPUID_8000_001E for AMD > > > > On Fri, Jun 08, 2018 at 06:56:17PM -0400, Babu Moger wrote: > > > Add support for cpuid leaf CPUID_8000_001E. Build the config that closely > > > match the underlying hardware. Please refer to the Processor Programming > > > Reference (PPR) for AMD Family 17h Model for more details. > > > > > > Signed-off-by: Babu Moger <babu.moger@xxxxxxx> > > [...] > > > + case 0x8000001E: > > > + assert(cpu->core_id <= 255); > > > > It is possible to trigger this assert using: > > > > $ qemu-system-x86_64 -machine q35,accel=kvm,kernel-irqchip=split -device > > intel-iommu,intremap=on,eim=on -smp > > 1,maxcpus=258,cores=258,threads=1,sockets=1 -cpu > > qemu64,xlevel=0x8000001e -device qemu64-x86_64-cpu,apic-id=257 > > qemu-system-x86_64: warning: Number of hotpluggable cpus requested (258) > > exceeds the recommended cpus supported by KVM (240) > > qemu-system-x86_64: > > /home/ehabkost/rh/proj/virt/qemu/target/i386/cpu.c:5888: cpu_x86_cpuid: > > Assertion `cpu->core_id <= 255' failed. > > Aborted (core dumped) > > > > See bug report and discussion at > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla. > > redhat.com%2Fshow_bug.cgi%3Fid%3D1834200&data=02%7C01%7Cbabu. > > moger%40amd.com%7C8a2724729b914bc9b53d08d8071db392%7C3dd8961fe4 > > 884e608e11a82d994e183d%7C0%7C0%7C637267171438806408&sdata=ib > > iGlF%2FF%2FVtYQLf7fe988kxFsLhj4GrRiTOq4LUuOT8%3D&reserved=0 > > > > Also, it looks like encode_topo_cpuid8000001e() assumes core_id > > has only 3 bits, so the existing assert() is not even sufficient. > > We need to decide what to do if the user requests nr_cores > 8. > > > > Probably omitting CPUID[0x8000001E] if the VCPU topology is > > incompatible with encode_topo_cpuid8000001e() (and printing a > > warning) is the safest thing to do right now. > > Eduardo, We need to generalize the encode_topo_cpuid8000001e decoding. > We will have to remove 3 bit limitation there. It will not scale with > latest configurations. I will take a look that. > > For now, best option I think is to(like you mentioned in bug 1834200), > declaring nr_cores > 256 as never supported (or deprecated); and throw > warning. > > What do you think? I believe we can declare nr_cores > 256 as never supported to address the assert failure. Other CPUID functions also look broken when nr_cores is too large: encode_cache_cpuid4() seems to assume nr_cores is 128 or less. But we still need to make nr_cores > 8 safe while encode_topo_cpuid8000001e() is not generalized yet. > > > > > > > > > + encode_topo_cpuid8000001e(cs, cpu, > > > + eax, ebx, ecx, edx); > > > + break; > > > case 0xC0000000: > > > *eax = env->cpuid_xlevel2; > > > *ebx = 0; > > > -- > > > 1.8.3.1 > > > > > > > -- > > Eduardo > -- Eduardo
