On Mon, Sep 14, 2015 at 11:43:27AM +0200, Ard Biesheuvel wrote: > On 14 September 2015 at 11:25, Mark Rutland <mark.rutland@xxxxxxx> wrote: > > On Sat, Sep 12, 2015 at 12:36:55PM +0100, Daniel Kiper wrote: > >> On Fri, Sep 11, 2015 at 05:25:59PM +0100, Mark Rutland wrote: > >> > On Fri, Sep 11, 2015 at 01:46:43PM +0100, Daniel Kiper wrote: > >> > > On Thu, Sep 10, 2015 at 05:23:02PM +0100, Mark Rutland wrote: > >> > >> [...] > >> > >> > > > 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? > >> > > >> > I don't want to. > >> > > >> > I asked "What can't be simulated?" because I assumed everything > >> > necessary/mandatory could be simulated without needinng access to any > >> > real EFI boot services. > >> > > >> > As far as I can see all that's necessary is to provide a compatible > >> > interface. > >> > >> Could you be more precise what do you need? Please enumerate. UEFI spec has > >> more than 2500 pages and I do not think that we need all stuff in dom0. > >> > >> > > What do you need from EFI boot services in dom0? > >> > > >> > The ability to call ExitBootServices() and SetVirtualAddressMap() on a > >> > _virtual_ address map for _virtual_ services provided by the hypervisor. > >> > >> I am confused. Why do you need that? Please remember, EFI is owned and > >> operated by Xen hypervisor. dom0 does not have direct access to EFI. > > > > Let's take a step back. > > > > My objection here is to passing the Dom0 kernel properties as if it were > > booted with direct access to a full UEFI, then later fixing that up > > (when Xen is detected and we apply its hypercall EFI implementation). > > > > To be honest, I don't think that has ever been suggested here. What > was suggested is to provide a minimal EFI like environment that allows > the post-stub EFI code to proceed and find the ACPI root pointer. > > > If the kernel cannot use EFI natively, why pretend to the kernel that it > > can? The hypercall implementation is _not_ EFI (though it provides > > access to some services). > > > > To get access to the ACPI root pointer, for which there is only one > specified way of obtaining it on ARM, which is via the UEFI > configuration table database > > > The two ways I can see providing Dom0 with EFI services are: > > > > * Have Xen create shims for any services, in which any hypercalls live, > > and pass these to the kernel with a virtual system table. This keeps > > the interface to the kernel the same regardless of Xen. > > > > * Have the kernel detect Xen EFI capability via Xen, without passing the > > usual native EFI parameters. This can then be installed into the > > kernel in a Xen-specific manner, and we know from the outset that > > Xen-specific caveats apply. > > > > As per my original email, I'm not against the renaming of the stub > > parameters if we standardise the rest of the details, but I believe > > that's orthogonal to the Xen Dom0 case. > > > > Xen will not boot the kernel via the stub, but directly. It needs to > supply a EFI like environment so that the kernel can boot via ACPI. > There is no reason whatsoever to mock up boot services or other pieces > of UEFI functionality that are not needed. The core kernel does not > call any boot services or SetVirtualAddressMap/ConvertPointer, and > there is already paravirtualized plumbing in place for the remaining > runtime services. > > Hence my claim earlier that we should cope with the runtime services > pointer being NULL, since that is really the only thing standing in I suppose that you thought about EFI_INVALID_TABLE_ADDR... > the way from the kernel side. If you feel that violates the spec in If yes then you should know that dom0 on x86 EFI platform works with efi.runtime == EFI_INVALID_TABLE_ADDR without any issue. So, I think that all problems are solved. Daniel -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
