On Fri, Sep 11, 2015 at 03:30:15PM +0200, Ard Biesheuvel wrote: > On 11 September 2015 at 15:14, Stefano Stabellini > <stefano.stabellini@xxxxxxxxxxxxx> wrote: > > On Fri, 11 Sep 2015, Daniel Kiper wrote: > >> On Thu, Sep 10, 2015 at 05:23:02PM +0100, Mark Rutland wrote: > >> > > > C) When you could go: > >> > > > > >> > > > DT -> Discover Xen -> Xen-specific stuff -> Xen-specific EFI/ACPI discovery > >> > > > >> > > I take you mean discovering Xen with the usual Xen hypervisor node on > >> > > device tree. I think that C) is a good option actually. I like it. Not > >> > > sure why we didn't think about this earlier. Is there anything EFI or > >> > > ACPI which is needed before Xen support is discovered by > >> > > arch/arm64/kernel/setup.c:setup_arch -> xen_early_init()? > >> > > >> > Currently lots (including the memory map). With the stuff to support > >> > SPCR, the ACPI discovery would be moved before xen_early_init(). > >> > > >> > > If not, we could just go for this. A lot of complexity would go away. > >> > > >> > I suspect this would still be fairly complex, but would at least prevent > >> > the Xen-specific EFI handling from adversely affecting the native case. > >> > > >> > > > D) If you want to be generic: > >> > > > EFI -> EFI application -> EFI tables -> ACPI tables -> Xen-specific stuff > >> > > > \------------------------------------------/ > >> > > > (virtualize these, provide shims to Dom0, but handle > >> > > > everything in Xen itself) > >> > > > >> > > I think that this is good in theory but could turn out to be a lot of > >> > > work in practice. We could probably virtualize the RuntimeServices but > >> > > the BootServices are troublesome. > >> > > >> > What's troublesome with the boot services? > >> > > >> > What can't be simulated? > >> > >> How do you want to access bare metal EFI boot services from dom0 if they > >> were shutdown long time ago before loading dom0 image? What do you need > >> from EFI boot services in dom0? > > > > That's right. Trying to emulate BootServices after the real > > ExitBootServices has already been called seems like a very bad plan. > > > > I think that whatever interface we come up with, would need to be past > > ExitBootServices. > > It feels like this discussion is going in circles. > > When we discussed this six months ago, we already concluded that, > since UEFI is the only specified way that the presence of ACPI is > advertised on an ARM system, we need to emulate UEFI to some extent. > > So we need the EFI system table to expose the UEFI configuration table > that carries the ACPI root pointer. > > Since ACPI support also relies on the UEFI memory map (I think?), we > need that as well. > > These two items are exactly what we pass via the UEFI DT properties, > so we should indeed promote the current de-facto binding to a proper > binding, and renaming the properties makes sense in that context. > > I agree that this should also include a description of the expected > state of the firmware, i.e., that ExitBootServices() has been called, > and that the memory map has been populated with virtual address, which > have been installed using SetVirtualAddressMap() if they differ from > the physical addresses. (The current implementation on the kernel side > is perfectly capable of dealing with a 1:1 mapping). > > Beyond that, there is no point in pretending to be a full UEFI > implementation, imo. Boot services are not required, nor are runtime > services (only the current EFI init code on arm needs to be modified > to deal with a NULL runtime services pointer) Taking into account above I think that you have most of the code in place. Please take a look at linux/arch/x86/xen/efi.c, linux/drivers/acpi/osl.c and linux/drivers/xen/efi.c (maybe somewhere else). In general you should create ARM version of xen_efi_init() (x86 version you can find in linux/drivers/xen/efi.c; it is very simple thing), maybe add some code in a few places and voila. Daniel -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
