Re: [Xen-devel] [PATCH RFC 1/8] x86/hvm: set initial apicid to vcpu_id

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.02.16 at 22:02, <joao.m.martins@xxxxxxxxxx> wrote:
> Currently the initial_apicid is set vcpu_id * 2 which makes it difficult
> for the toolstack to manage how is the topology seen by the guest.
> Instead of forcing procpkg and proccount to be VCPUID * 2, instead we
> set it to max vcpuid on proccount to max_vcpu_id + 1 (logical number of
> logical cores) and procpkg to max_vcpu_id (max cores minus 1)

I'm afraid it takes more than this to explain why the change is
needed or at least desirable. In particular I'd like to suggest that
you do some archeology to understand why things are the way
they are.

> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -4633,7 +4633,7 @@ void hvm_cpuid(unsigned int input, unsigned int *eax, 
> unsigned int *ebx,
>      case 0x1:
>          /* Fix up VLAPIC details. */
>          *ebx &= 0x00FFFFFFu;
> -        *ebx |= (v->vcpu_id * 2) << 24;
> +        *ebx |= (v->vcpu_id) << 24;
>          if ( vlapic_hw_disabled(vcpu_vlapic(v)) )
>              __clear_bit(X86_FEATURE_APIC & 31, edx);

In no case is this sufficient as adjustment to the hypervisor side,
as it gets things out of sync with e.g. hvm/vlapic.c.

Jan


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