Re: [XEN][PATCH 2/8] xen/arm: move vcpu_switch_to_aarch64_mode() in arch_vcpu_create()

[Julien Grall <julien@xxxxxxx>]

Hi,

On 23/07/2025 08:58, Grygorii Strashko wrote:
> From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
>
> Move vcpu_switch_to_aarch64_mode() in arch_vcpu_create() callback instead
> of calling it manually from few different places after vcpu_create().
>
> Before doing above ensure vcpu0 is created after kernel_probe() is done and
> domain's guest execution mode (32-bit/64-bit) is set for dom0 and dom0less
> domains.
The commit message doesn't mention anything about domains created by the 
toolstack. In this case, from my understanding, the switch to 64-bit 
domain happens *after* the vCPUs are created.
At the moment, I think this is probably ok to call...

> Signed-off-by: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
> ---
>   xen/arch/arm/domain.c                    |  3 +++
>   xen/arch/arm/domain_build.c              | 13 +++++--------
>   xen/common/device-tree/dom0less-build.c  |  6 +++---
>   xen/include/asm-generic/dom0less-build.h |  2 +-
>   4 files changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> index 79a144e61be9..bbd4a764c696 100644
> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -586,6 +586,9 @@ int arch_vcpu_create(struct vcpu *v)
>       if ( get_ssbd_state() == ARM_SSBD_RUNTIME )
>           v->arch.cpu_info->flags |= CPUINFO_WORKAROUND_2_FLAG;
>   
> +    if ( is_64bit_domain(v->domain) )
> +        vcpu_switch_to_aarch64_mode(v);
... this function here because I *think* it would be NOP. But this feels 
really fragile.
If the desire is to make 32-bit domain optional on Arm64. Then I think 
it would be better to pass the domain type when the domain is created 
(IOW add an extra flags to XEN_DOMCTL_createdomain). This will require 
more work, but it will be a lot more robust.
Cheers,

--
Julien Grall