Re: [PATCH v13 1/5] i386: Add support for CPUID_8000_001E for AMD

[Eduardo Habkost <ehabkost@redhat.com>]

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@amd.com>
[...]
> +    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://bugzilla.redhat.com/show_bug.cgi?id=1834200

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.



> +        encode_topo_cpuid8000001e(cs, cpu,
> +                                  eax, ebx, ecx, edx);
> +        break;
>      case 0xC0000000:
>          *eax = env->cpuid_xlevel2;
>          *ebx = 0;
> -- 
> 1.8.3.1
> 

-- 
Eduardo