[RFC PATCH v1 3/8] KVM: selftests: Add virt_arch_ucall_prealloc() arch specific implementation

[Sean Christopherson <seanjc@google.com>]

On Thu, Nov 02, 2023, Zeng Guang wrote:
> diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> index a18db6a7b3cf..dbaa2cf83c1c 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> @@ -917,6 +917,23 @@ static inline void virt_dump(FILE *stream, struct kvm_vm *vm, uint8_t indent)
>  	virt_arch_dump(stream, vm, indent);
>  }
>  
> +/*
> + * Virtual UCALL memory pre-processing
> + *
> + * Input Args:
> + *   ucall_gva - Guest virtual address point to memory of ucall pool
> + *
> + * Output Args: None
> + *
> + * Return:
> + *   Processed guest virtual address point to memory of ucall pool
> + */

Please omit the massive comments, they are yet another misguided remnant in
selftests that we are purging.

> diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> index 6f4295a13d00..525b714ee13c 100644
> --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
> +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> @@ -388,6 +388,18 @@ void virt_arch_dump(FILE *stream, struct kvm_vm *vm, uint8_t indent)
>  	}
>  }
>  
> +void *virt_arch_ucall_prealloc(uint64_t ucall_gva)
> +{
> +	unsigned short desc_cs;
> +
> +	asm volatile ("mov %%cs,%0" :  "=r" (desc_cs));

Strictly speaking, CS.DPL is not the source of truth for CPL, SS.DPL is.  But
that's probably a moot point, because I again think this is a hack that shows the
overall approach isn't maintainable.

Can you post the actual usage of userspace selftests, i.e. the "full" series?
It's really hard to build a mental model of how this all fits together without
seeing the actual usage.