Re: [Qemu-devel] [FIX] X86 CPU topology broken in KVM mode

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-09-07 06:21, Bharata B Rao wrote:
> Hi,
> 
> Sometime back I posted a patch for fixing x86 CPU topology (
> http://lists.gnu.org/archive/html/qemu-devel/2011-08/msg02022.html).
> Here is the next version of the fix which addresses all but one
> comment received during that post.
> 
> - Fixed code style issues
> - Ensured that the fix doesn't break TCG mode
> - I am not sure what is the problem with i486 as I haven't been able
> to boot an i486 VM successfully, hence haven't attempted to fix this.

-smp 2 -cpu i486 boots fine here (granted, I don't have some i486 SMP
kernel at hand).

> 
> I have tested following scenarios and found the fix to be working fine.
> 
> KVM: (with --enable-kvm)
> -smp sockets=1,cores=4,threads=2
> -smp sockets=4,cores=4,threads=2
> -cpu core2duo sockets=1,cores=4,threads=2
> -cpu core2duo sockets=2,cores=4,threads=2
> 
> TCG: (without --enable-kvm)
> -cpu core2duo sockets=1,cores=4,threads=2
> -cpu core2duo sockets=2,cores=4,threads=2
> 
> Here is the updated patch which now applies against qemu.git.
> 
> ********************
> 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. This is done by moving the setting of cpuid_apic_id
> to cpu_x86_init() where it will work for both KVM as well as TCG modes.
> 
> Signed-off-by: Bharata B Rao <bharata.rao@gmail.com>
> ---
>  hw/pc.c              |    1 -
>  target-i386/helper.c |    5 +++++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> Index: qemu/hw/pc.c
> ===================================================================
> --- qemu.orig/hw/pc.c
> +++ qemu/hw/pc.c
> @@ -933,7 +933,6 @@ static CPUState *pc_new_cpu(const char *
>          exit(1);
>      }
>      if ((env->cpuid_features & CPUID_APIC) || smp_cpus > 1) {
> -        env->cpuid_apic_id = env->cpu_index;
>          env->apic_state = apic_init(env, env->cpuid_apic_id);
>      }
>      qemu_register_reset(pc_cpu_reset, env);
> Index: qemu/target-i386/helper.c
> ===================================================================
> --- qemu.orig/target-i386/helper.c
> +++ qemu/target-i386/helper.c
> @@ -1256,6 +1256,11 @@ CPUX86State *cpu_x86_init(const char *cp
>          cpu_x86_close(env);
>          return NULL;
>      }
> +
> +    if (env->cpuid_features & CPUID_APIC) {

|| smp_cpus > 1

Should be obvious when looking at the hunk you took this from.

> +        env->cpuid_apic_id = env->cpu_index;
> +    }
> +
>      mce_init(env);
> 
>      qemu_init_vcpu(env);
> *************************
> 
> Regards,
> Bharata.
> --
>  http://bharata.sulekha.com/blog/posts.htm, http://raobharata.wordpress.com/
> 
> 

Jan

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