On Mon, 14 Sep 2015, Mark Rutland 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). > > 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). > > 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. A not a fan of three-point estimates, so I am just going to say that "this looks like a lot of work". Also emulating services is known to be prone to errors. > * 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. I prefer this approach by far. In the future we might have to move the xen_early_init call earlier (before ACPI and EFI Runtime Services get initialized). > 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. -- 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
