Re: [Xen-devel] [PATCH v3 17/17] xen/arm: vpsci: Rework the logic to start AArch32 vCPU in Thumb mode

[Andre Przywara <andre.przywara@xxxxxxxxxx>]

Hi,

On 15/02/18 15:02, Julien Grall wrote:
> 32-bit domain is able to select the instruction (ARM vs Thumb) to use
> when boot a new vCPU via CPU_ON. This is indicated via bit[0] of the
> entry point address (see "T32 support" in PSCI v1.1 DEN0022D). bit[0]
> must be cleared when setting the PC.
> 
> At the moment, Xen is setting the CPSR.T but never clear bit[0]. Clear
> it to match the specification.

Yes, that is the right thing to do, as the spec requires this.

> At the same time, slighlty rework the code to make clear thumb is only for
> 32-bit domain. Lastly, take the opportunity to switch is_thumb from int
> to bool.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>

Cheers,
Andre.

> 
> ---
>     Changes in v3:
>         - Patch added
> ---
>  xen/arch/arm/vpsci.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/arm/vpsci.c b/xen/arch/arm/vpsci.c
> index 1729f7071e..9f4e5b8844 100644
> --- a/xen/arch/arm/vpsci.c
> +++ b/xen/arch/arm/vpsci.c
> @@ -28,7 +28,7 @@ static int do_common_cpu_on(register_t target_cpu, 
> register_t entry_point,
>      struct domain *d = current->domain;
>      struct vcpu_guest_context *ctxt;
>      int rc;
> -    int is_thumb = entry_point & 1;
> +    bool is_thumb = entry_point & 1;
>      register_t vcpuid;
>  
>      vcpuid = vaffinity_to_vcpuid(target_cpu);
> @@ -62,6 +62,13 @@ static int do_common_cpu_on(register_t target_cpu, 
> register_t entry_point,
>      if ( is_32bit_domain(d) )
>      {
>          ctxt->user_regs.cpsr = PSR_GUEST32_INIT;
> +        /* Start the VCPU with THUMB set if it's requested by the kernel */
> +        if ( is_thumb )
> +        {
> +            ctxt->user_regs.cpsr |= PSR_THUMB;
> +            ctxt->user_regs.pc64 &= ~(u64)1;
> +        }
> +
>          ctxt->user_regs.r0_usr = context_id;
>      }
>  #ifdef CONFIG_ARM_64
> @@ -71,10 +78,6 @@ static int do_common_cpu_on(register_t target_cpu, 
> register_t entry_point,
>          ctxt->user_regs.x0 = context_id;
>      }
>  #endif
> -
> -    /* Start the VCPU with THUMB set if it's requested by the kernel */
> -    if ( is_thumb )
> -        ctxt->user_regs.cpsr |= PSR_THUMB;
>      ctxt->flags = VGCF_online;
>  
>      domain_lock(d);
> 

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