Re: [PATCH v4 03/13] KVM: arm64: nVHE: Simplify __guest_exit_panic path

[Will Deacon <will@kernel.org>]

On Wed, May 29, 2024 at 01:12:09PM +0100, Pierre-Clément Tosi wrote:
> In invalid_host_el2_vect (i.e. EL2{t,h} handlers in nVHE guest context),

*guest* context? Are you sure?

> remove the duplicate vCPU context check that __guest_exit_panic also
> performs, allowing an unconditional branch to it.
> 
> Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/host.S | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
> index 135cfb294ee5..71fb311b4c0e 100644
> --- a/arch/arm64/kvm/hyp/nvhe/host.S
> +++ b/arch/arm64/kvm/hyp/nvhe/host.S
> @@ -197,18 +197,13 @@ SYM_FUNC_END(__host_hvc)
>  	sub	x0, sp, x0			// x0'' = sp' - x0' = (sp + x0) - sp = x0
>  	sub	sp, sp, x0			// sp'' = sp' - x0 = (sp + x0) - x0 = sp
>  
> -	/* If a guest is loaded, panic out of it. */
> -	stp	x0, x1, [sp, #-16]!
> -	get_loaded_vcpu x0, x1
> -	cbnz	x0, __guest_exit_panic
> -	add	sp, sp, #16

I think this is actually dead code and we should just remove it. AFAICT,
invalid_host_el2_vect is only used for the host vectors and the loaded
vCPU will always be NULL, so this is pointless. set_loaded_vcpu() is
only called by the low-level guest entry/exit code and with the guest
EL2 vectors installed.

> -
>  	/*
>  	 * The panic may not be clean if the exception is taken before the host
>  	 * context has been saved by __host_exit or after the hyp context has
>  	 * been partially clobbered by __host_enter.
>  	 */
> -	b	hyp_panic
> +	stp	x0, x1, [sp, #-16]!
> +	b	__guest_exit_panic

In which case, this should just be:

	add	sp, sp, #16
	b	hyp_panic

Did I miss something?

Will

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