Re: [Qemu-devel] X86 CPU topology broken in qemu ?

[Jan Kiszka]

On 2011-08-17 07:25, Bharata B Rao wrote:
> Hi,
> 
> I see that x86 CPU topology inside VM is not showing up as specified.
> With some debugging, I found out that the root cause for this: qemu is
> not enumerating the apic ids correctly for vcpus. I made the below
> hackish change to get it working.  Has anybody else seen this problem
> ?  This patch is on qemu-kvm-0.14.1. Using 2.6.39 for guest.
> 
> ***************************
> Fix apic id enumeration
> 
> apic id returned to guest kernel in ebx for cpuid(function=1) depends on
> CPUX86State->cpuid_apic_id which gets populated after the cpuid information
> is cached in the host kernel.
> 
> Fix this by setting cpuid_apic_id before cpuid information is passed to
> the host kernel.
> 
> Signed-off-by: Bharata B Rao <address@hidden>
> ---
>  hw/pc.c           |    4 +---
>  target-i386/kvm.c |    3 +++
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> Index: qemu-kvm-0.14.1/hw/pc.c
> ===================================================================
> --- qemu-kvm-0.14.1.orig/hw/pc.c
> +++ qemu-kvm-0.14.1/hw/pc.c
> @@ -930,10 +930,8 @@ CPUState *pc_new_cpu(const char *cpu_mod
>         fprintf(stderr, "Unable to find x86 CPU definition\n");
>         exit(1);
>     }
> -    if ((env->cpuid_features & CPUID_APIC) || smp_cpus > 1) {
> -        env->cpuid_apic_id = env->cpu_index;
> +    if ((env->cpuid_features & CPUID_APIC) || smp_cpus > 1)
>         env->apic_state = apic_init(env, env->cpuid_apic_id);
> -    }
>     qemu_register_reset(pc_cpu_reset, env);
>     pc_cpu_reset(env);
>     return env;
> Index: qemu-kvm-0.14.1/target-i386/kvm.c
> ===================================================================
> --- qemu-kvm-0.14.1.orig/target-i386/kvm.c
> +++ qemu-kvm-0.14.1/target-i386/kvm.c
> @@ -340,6 +340,9 @@ int kvm_arch_init_vcpu(CPUState *env)
> 
>     cpuid_i = 0;
> 
> +    if (env->cpuid_features & CPUID_APIC)
> +        env->cpuid_apic_id = env->cpu_index;
> +

Moving it only here will break TCG mode. Make sure to test both. I guess
it's best to move cpuid_apic_id initialization into cpu_x86_init. And
you need to take care of the external APIC case (i486) as well.

Jan

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