Re: [Xen-devel] [PATCH 2/4] xen/arm: read ACTLR on the pcpu where the vcpu will run

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 15/02/18 23:16, Stefano Stabellini wrote:
> On big.LITTLE systems not all cores have the same ACTLR. Instead of
> reading ACTLR and setting v->arch.actlr in vcpu_initialise, which is run
> always on pcpu 0, do it later on the same pcpu where the vcpu will run.
While the Hardware domain vCPUs will always be created on pCPU 0, this 
may not be the case for other domain as it is done via an hypercall.
> This way, assuming that the vcpu has been created with the right pcpu
> affinity, the guest will be able to read the right ACTLR value, matching
> the one of the physical cpu.
>
> Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> ---
>   xen/arch/arm/domain.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> index a010443..532e824 100644
> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -314,6 +314,8 @@ static void schedule_tail(struct vcpu *prev)
>   
>   static void continue_new_vcpu(struct vcpu *prev)
>   {
> +    current->arch.actlr = READ_SYSREG32(ACTLR_EL1);
This is not enough, you also need to move the call of 
processor_vcpu_initialise here. For instance on Cortex-A15, this will 
set/clear the SMP bit in ACTLR.
Also, I just noticed that processor_vcpu_initialize (in 
arch/arm/processor.c) assumes all the processor will be the same.  We 
probably want to turn the variable processor into a per-cpu value.
> +
>       schedule_tail(prev);
>   
>       if ( is_idle_vcpu(current) )
> @@ -540,8 +542,6 @@ int vcpu_initialise(struct vcpu *v)
>   
>       v->arch.vmpidr = MPIDR_SMP | vcpuid_to_vaffinity(v->vcpu_id);
>   
> -    v->arch.actlr = READ_SYSREG32(ACTLR_EL1);
> -
>       v->arch.hcr_el2 = get_default_hcr_flags();
>   
>       processor_vcpu_initialise(v);
Cheers,

--
Julien Grall

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