Re: [PATCH v2 16/16] ARM64: XEN: Initialize Xen specific UEFI runtime services

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Mon, 18 Jan 2016, Mark Rutland wrote:
> On Mon, Jan 18, 2016 at 05:45:24PM +0000, Stefano Stabellini wrote:
> > On Mon, 18 Jan 2016, Mark Rutland wrote:
> > > On Fri, Jan 15, 2016 at 02:55:29PM +0800, Shannon Zhao wrote:
> > > > +void __init xen_efi_runtime_setup(void)
> > > > +{
> > > > +	efi.get_time                 = xen_efi_get_time;
> > > > +	efi.set_time                 = xen_efi_set_time;
> > > > +	efi.get_wakeup_time          = xen_efi_get_wakeup_time;
> > > > +	efi.set_wakeup_time          = xen_efi_set_wakeup_time;
> > > > +	efi.get_variable             = xen_efi_get_variable;
> > > > +	efi.get_next_variable        = xen_efi_get_next_variable;
> > > > +	efi.set_variable             = xen_efi_set_variable;
> > > > +	efi.query_variable_info      = xen_efi_query_variable_info;
> > > > +	efi.update_capsule           = xen_efi_update_capsule;
> > > > +	efi.query_capsule_caps       = xen_efi_query_capsule_caps;
> > > > +	efi.get_next_high_mono_count = xen_efi_get_next_high_mono_count;
> > > > +	efi.reset_system             = NULL;
> > > > +}
> > > 
> > > How do capsules work in the absence of an EFI system reset?
> > 
> > Actually I don't think that capsules are available in Xen on ARM64 yet,
> > see "TODO - disabled until implemented on ARM" in
> > xen/common/efi/runtime.c.
> > 
> > FYI system reset is available, but it is provided via a different
> > mechanism (HYPERVISOR_sched_op(xen_restart...)
> 
> Will that trigger Xen to do the right thing to trigger capsule updates
> when implemented in Xen? Or do we need a xen_efi_reset_system?

On ARM, to reboot the hardware, Xen calls the native PSCI system_reset
method. On x86, Xen calls efi_reset_system on EFI systems, and has
several fall backs if that doesn't work as expected (see
xen/arch/x86/shutdown.c:machine_restart).

But on a second look it doesn't look like that the capsule hypercalls
are implemented correctly even on x86 (there is an "XXX fall through for
now" comment in the code). I guess they are not available on Xen at all
unfortunately.


> Does that override PSCI?

It does not, HYPERVISOR_sched_op(xen_restart,) is in addition to it. It
ends up calling the same function within Xen as PSCI system_reset.


> In machine_restart we try efi_reboot first specifically to allow for
> capsule updates. Similarly drivers/firmware/efi/reboot.c registers
> efi_power_off late in order to override anything else, though that's
> best-effort at present.

That's very interesting. I think that Xen on ARM should follow what
Linux does and what Xen already does on x86 and try efi_reset_system
first on efi systems.