Re: [PATCH v2] arm64: KVM: Register CPU notifiers when the kernel runs at HYP

[Christoffer Dall <christoffer.dall@linaro.org>]

On Wed, Mar 30, 2016 at 06:33:04PM +0100, James Morse wrote:
> When the kernel is running at EL2, it doesn't need init_hyp_mode() to
> configure page tables for HYP. This function also registers the CPU
> hotplug and lower power notifiers that cause HYP to be re-initialised
> after the CPU has been reset.
> 
> To avoid losing the register state that controls stage2 translation, move
> the registering of these notifiers into init_subsystems(), and add a
> is_kernel_in_hyp_mode() path to each callback.

I had naively, or perhaps supidly, assumed that a VHE kernel would
save/restore all EL2 state as part of its suspend/resume procedure, but
I guess that wouldn't work for hotplug anyway.

In any case:

Acked-by: Christoffer Dall <christoffer.dall@linaro.org>

And applied.

Thanks,
-Christoffer

> 
> Fixes: 1e947bad0b6 ("arm64: KVM: Skip HYP setup when already running in HYP")
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> 
> Change since v1:
>  * Moved common re-init code to cpu_hyp_reinit().
> 
>  arch/arm/kvm/arm.c | 52 +++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 33 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 6accd66d26f0..b5384311dec4 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -1061,15 +1061,27 @@ static void cpu_init_hyp_mode(void *dummy)
>  	kvm_arm_init_debug();
>  }
>  
> +static void cpu_hyp_reinit(void)
> +{
> +	if (is_kernel_in_hyp_mode()) {
> +		/*
> +		 * cpu_init_stage2() is safe to call even if the PM
> +		 * event was cancelled before the CPU was reset.
> +		 */
> +		cpu_init_stage2(NULL);
> +	} else {
> +		if (__hyp_get_vectors() == hyp_default_vectors)
> +			cpu_init_hyp_mode(NULL);
> +	}
> +}
> +
>  static int hyp_init_cpu_notify(struct notifier_block *self,
>  			       unsigned long action, void *cpu)
>  {
>  	switch (action) {
>  	case CPU_STARTING:
>  	case CPU_STARTING_FROZEN:
> -		if (__hyp_get_vectors() == hyp_default_vectors)
> -			cpu_init_hyp_mode(NULL);
> -		break;
> +		cpu_hyp_reinit();
>  	}
>  
>  	return NOTIFY_OK;
> @@ -1084,9 +1096,8 @@ static int hyp_init_cpu_pm_notifier(struct notifier_block *self,
>  				    unsigned long cmd,
>  				    void *v)
>  {
> -	if (cmd == CPU_PM_EXIT &&
> -	    __hyp_get_vectors() == hyp_default_vectors) {
> -		cpu_init_hyp_mode(NULL);
> +	if (cmd == CPU_PM_EXIT) {
> +		cpu_hyp_reinit();
>  		return NOTIFY_OK;
>  	}
>  
> @@ -1128,6 +1139,22 @@ static int init_subsystems(void)
>  	int err;
>  
>  	/*
> +	 * Register CPU Hotplug notifier
> +	 */
> +	cpu_notifier_register_begin();
> +	err = __register_cpu_notifier(&hyp_init_cpu_nb);
> +	cpu_notifier_register_done();
> +	if (err) {
> +		kvm_err("Cannot register KVM init CPU notifier (%d)\n", err);
> +		return err;
> +	}
> +
> +	/*
> +	 * Register CPU lower-power notifier
> +	 */
> +	hyp_cpu_pm_init();
> +
> +	/*
>  	 * Init HYP view of VGIC
>  	 */
>  	err = kvm_vgic_hyp_init();
> @@ -1270,19 +1297,6 @@ static int init_hyp_mode(void)
>  	free_boot_hyp_pgd();
>  #endif
>  
> -	cpu_notifier_register_begin();
> -
> -	err = __register_cpu_notifier(&hyp_init_cpu_nb);
> -
> -	cpu_notifier_register_done();
> -
> -	if (err) {
> -		kvm_err("Cannot register HYP init CPU notifier (%d)\n", err);
> -		goto out_err;
> -	}
> -
> -	hyp_cpu_pm_init();
> -
>  	/* set size of VMID supported by CPU */
>  	kvm_vmid_bits = kvm_get_vmid_bits();
>  	kvm_info("%d-bit VMID\n", kvm_vmid_bits);
> -- 
> 2.8.0.rc3
>