[PATCH 2/3] KVM: ARM: Fix calculation of virtual CPU ID

[Christoffer Dall]

On Thu, Sep 26, 2013 at 04:49:27PM +0100, Jonathan Austin wrote:
> KVM does not have a notion of multiple clusters for CPUs, just a linear
> array of CPUs. When using a system with cores in more than one cluster, the
> current method for calculating the virtual MPIDR will leak the (physical)
> cluster information into the virtual MPIDR. One effect of this is that
> Linux under KVM fails to boot multiple CPUs that aren't in the 0th cluster.
> 
> This patch does away with exposing the real MPIDR fields in favour of simply
> using the virtual CPU number (but preserving the U bit, as before).
> 
> Signed-off-by: Jonathan Austin <jonathan.austin at arm.com>
> Acked-by: Marc Zyngier <marc.zyngier at arm.com>
> ---
>  arch/arm/kvm/coproc_a15.c |   11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm/kvm/coproc_a15.c b/arch/arm/kvm/coproc_a15.c
> index cf93472..bbd4b88 100644
> --- a/arch/arm/kvm/coproc_a15.c
> +++ b/arch/arm/kvm/coproc_a15.c
> @@ -27,14 +27,11 @@
>  static void reset_mpidr(struct kvm_vcpu *vcpu, const struct coproc_reg *r)
>  {
>  	/*
> -	 * Compute guest MPIDR:
> -	 * (Even if we present only one VCPU to the guest on an SMP
> -	 * host we don't set the U bit in the MPIDR, or vice versa, as
> -	 * revealing the underlying hardware properties is likely to
> -	 * be the best choice).
> +	 * Compute guest MPIDR. No need to mess around with different clusters
> +	 * but we read the 'U' bit from the underlying hardware directly.
>  	 */
> -	vcpu->arch.cp15[c0_MPIDR] = (read_cpuid_mpidr() & ~MPIDR_LEVEL_MASK)
> -		| (vcpu->vcpu_id & MPIDR_LEVEL_MASK);
> +	vcpu->arch.cp15[c0_MPIDR] = (read_cpuid_mpidr() & MPIDR_SMP_BITMASK)
> +					| vcpu->vcpu_id;
>  }
>  
>  #include "coproc.h"
> -- 
> 1.7.9.5
> 
> 
Makes sense.

ack.

-Christoffer