[PATCH] arm64/efi: use UEFI ResetSystem() Runtime Service for system reset

[Mark Rutland]

Hi Ard,

On Thu, Mar 05, 2015 at 12:51:11PM +0000, Ard Biesheuvel wrote:
> If UEFI Runtime Services are available, the ResetSystem() service should
> be preferred over direct PSCI calls or other methods to reset the system.
> The reason is that the UpdateCapsule() UEFI Runtime Service, which is used
> to perform firmware updates, relies on this.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
> I sent roughly the same patch ~6 months ago, but at the time, we were still
> waiting for the restart notifier call chain patches to land. Since that code
> got rejected, I am proposing this again. Note that efi_enabled(x) always
> evaluates to 'false' on !CONFIG_EFI.

Also, efi_reboot is a static inline for !CONFIG_EFI, so I can't see any
possibility of a build failure.

> This fixes reboot on my Seattle [although it doesn't make it any faster :-)]
> 
>  arch/arm64/kernel/process.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index fde9923af859..a52bc0c316a8 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -21,6 +21,7 @@
>  #include <stdarg.h>
>  
>  #include <linux/compat.h>
> +#include <linux/efi.h>
>  #include <linux/export.h>
>  #include <linux/sched.h>
>  #include <linux/kernel.h>
> @@ -150,6 +151,14 @@ void machine_restart(char *cmd)
>  	local_irq_disable();
>  	smp_send_stop();
>  
> +	/*
> +	 * Prefer reboot via EFI if available, so that capsule updates [which
> +	 * rely on UEFI's ResetSystem() being called with the return value of
> +	 * UpdateCapsule()] have a chance of working as expected.
> +	 */
> +	if (efi_enabled(EFI_RUNTIME_SERVICES))
> +		efi_reboot(reboot_mode, NULL);

I expect that the particulars of the UpdateCapsule() will be handled
within efi_reboot and won't require any additions here. So the comment
could just be trimmed to say that UpdateCapsule() depends on the system
being reset with ResetSystem().

Also, we need to make sure we call efi_poweroff to make UpdateCapsule()
work when shutting the machine down (behind the scenes efi_poweroff
calls ResetSystem(EfiResetShutdown, ...)).

For that I think adding the following to arch/arm64/kernel/efi.c is
sufficient:

/*
 * UpdateCapsule() depends on the system being shutdown via
 * ResetSystem().
 */
bool efi_poweroff_required(void)
{
	return efi_enabled(EFI_RUNTIME_SERVICES);
}

I've given the patch a spin (with and without that addition) on Juno and
Seattle. So with that folded in:

Tested-by: Mark Rutland <mark.rutland at arm.com>
Reviewed-by: Mark Rutland <mark.rutland at arm.com>

Thanks,
Mark.