Re: [PATCH v4 05/28] arm64: KVM: Implement HVC_RESET_VECTORS stub hypercall in the init code

[Christoffer Dall <cdall@linaro.org>]

On Tue, Mar 21, 2017 at 07:20:35PM +0000, Marc Zyngier wrote:
> In order to restore HYP mode to its original condition, KVM currently
> implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
> defined API, it becomes necessary to implement HVC_RESET_VECTORS.
> 
> This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
> code, which so far lacked any form of hypercall support.
> 
> Reviewed-by: James Morse <james.morse@arm.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/kvm/hyp-init.S | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> index 6b29d3d9e1f2..6cf98ccd10f2 100644
> --- a/arch/arm64/kvm/hyp-init.S
> +++ b/arch/arm64/kvm/hyp-init.S
> @@ -22,6 +22,7 @@
>  #include <asm/kvm_mmu.h>
>  #include <asm/pgtable-hwdef.h>
>  #include <asm/sysreg.h>
> +#include <asm/virt.h>
>  
>  	.text
>  	.pushsection	.hyp.idmap.text, "ax"
> @@ -58,6 +59,9 @@ __invalid:
>  	 * x2: HYP vectors
>  	 */
>  __do_hyp_init:
> +	/* Check for a stub HVC call */
> +	cmp	x0, #HVC_STUB_HCALL_NR
> +	b.lo	__kvm_handle_stub_hvc
>  
>  	msr	ttbr0_el2, x0
>  
> @@ -119,6 +123,9 @@ __do_hyp_init:
>  	eret
>  ENDPROC(__kvm_hyp_init)
>  
> +ENTRY(__kvm_handle_stub_hvc)
> +	cmp	x0, #HVC_RESET_VECTORS
> +	b.ne	1f
>  	/*
>  	 * Reset kvm back to the hyp stub.
>  	 */
> @@ -133,9 +140,14 @@ ENTRY(__kvm_hyp_reset)
>  	/* Install stub vectors */
>  	adr_l	x0, __hyp_stub_vectors
>  	msr	vbar_el2, x0
> +	b	exit
>  
> +1:	mov	x0, #-1

nit: do we have the -1 return value documented somewhere and should we
define it as HVC_SUB_ERR_RETURN or something like that?

> +
> +exit:
>  	eret
>  ENDPROC(__kvm_hyp_reset)
> +ENDPROC(__kvm_handle_stub_hvc)
>  
>  	.ltorg
>  
> -- 
> 2.11.0
> 

Thanks,
-Christoffer