Re: [Xen-devel] [PATCH v2 4/6] xen/arm: make vpidr per vcpu

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 19/02/18 21:58, Stefano Stabellini wrote:
> On big.LITTLE systems not all cores have the same midr. Instead of
> storing only one vpidr per domain, make it per vcpu and initialize it to
> the value of the midr of the pcpu where the vcpu will run.
>
> This way, assuming that the vcpu has been created with the right pcpu
> affinity, the guest will be able to read the right vpidr value, matching
> the one of the physical cpu.
>
> Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>
> ---
>
> - remove warning message
> - make vpidr per vcpu
> ---
>   xen/arch/arm/domain.c        | 6 ++----
>   xen/arch/arm/vcpreg.c        | 4 ++--
>   xen/include/asm-arm/domain.h | 6 +++---
>   3 files changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> index fb51415..41d5d25 100644
> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -180,7 +180,7 @@ static void ctxt_switch_to(struct vcpu *n)
>   
>       p2m_restore_state(n);
>   
> -    WRITE_SYSREG32(n->domain->arch.vpidr, VPIDR_EL2);
> +    WRITE_SYSREG32(n->arch.vpidr, VPIDR_EL2);
Do we really need to store the vpidr in struct vcpu? It would be simpler 
and more efficient (no memory access) to use directly read MDIR_EL1 and 
copy it to VPIDR_EL1.
Cheers,

--
Julien Grall

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