[RFC PATCH] arm64/efi: use stable virtual mappings for UEFI runtime services

[Mark Rutland]

On Tue, Oct 14, 2014 at 03:17:21AM +0100, Dave Young wrote:
> Hi, Geoff
> 
> On 10/13/14 at 03:52pm, Geoff Levand wrote:
> > Hi Ard,
> > 
> > On Wed, 2014-10-08 at 19:38 +0200, Ard Biesheuvel wrote:
> > > I haven't tested this code under kexec myself, but I have confirmed that
> > > the runtime services work as expected (rtc-efi and efivars). The comments
> > > that Mark Salter and Will Deacon gave on the id mapping patch here
> > 
> > I applied this patch to my kexec master branch [1] and tested a basic
> > kexec re-boot using the FVP_Base_AEMv8A-AEMv8A_0.8_5602 model and the
> > 14.09 LEG EFI build.
> > 
> > It crashes when the 2nd stage kernel is starting up on the first
> > dereference of the c16 variable in uefi_init():
> > 
> >   c16 = early_memremap(efi.systab->fw_vendor, sizeof(vendor));
> >   if (c16) {
> >     for (i = 0; i < (int) sizeof(vendor) - 1 && *c16; ++i) {
> >                                                 ^^^^ crashes here
> > 
> > early_memremap() returns 0xFFFFFFBFFBCBF618, and the dereference
> > starts the crash.  I did not look into it further.
> 
> This is an expected behaviour as I mentioned before, we need save fw_vendor
> and the other two physical addresses and pass them to 2nd kernel.
> 
> UEFI firmware will convert them to virtual address after entering virtual mode.

So long as we know they are virtual addresses (implied by whatever way
we detect we're in virtual mode), and we know the virt->phys mappings
(which are in the EFI memmap passed via the DTB), we should be able to
figure out those physical addresses without having to pass them
explicitly, regardless of what mapping is used.

Mark.