On Mon, 28 Jan 2019 at 19:04, Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx> wrote: > > On 1/26/2019 3:22 AM, Ard Biesheuvel wrote: > > The UEFI spec revision 2.7 errata A section 8.4 has the following to > > say about the virtual memory runtime services: > > > > "This section contains function definitions for the virtual memory > > support that may be optionally used by an operating system at runtime. > > If an operating system chooses to make EFI runtime service calls in a > > virtual addressing mode instead of the flat physical mode, then the > > operating system must use the services in this section to switch the > > EFI runtime services from flat physical addressing to virtual > > addressing." > > > > So it is pretty clear that calling SetVirtualAddressMap() is entirely > > optional, and so there is no point in doing so unless it achieves > > anything useful for us. > > > > This is not the case for 64-bit ARM. The native mapping used by the OS > > is arbitrarily converted into another permutation of userland addresses > > (i.e., bits [63:48] cleared), and the runtime code could easily deal > > with the original layout in exactly the same way as it deals with the > > converted layout. However, due to constraints related to page size > > differences if the OS is not running with 4k pages, and related to > > systems that may expose the individual sections of PE/COFF runtime > > modules as different memory regions, creating the virtual layout is a > > bit fiddly, and requires us to sort the memory map and reason about > > adjacent regions with identical memory types etc etc. > > > > So the obvious fix is to stop calling SetVirtualAddressMap() altogether > > on arm64 systems. However, to avoid surprises, which are notoriously > > hard to diagnose when it comes to OS<->firmware interactions, let's > > start by making it an opt-out feature, and implement support for the > > 'efi=novamap' kernel command line parameter on ARM and arm64 systems. > > > > (Note that 32-bit ARM generally does require SetVirtualAddressMap() to be > > used, given that the physical memory map and the kernel virtual address > > map are not guaranteed to be non-overlapping like on arm64. However, > > having support for efi=novamap,noruntime on 32-bit ARM, combined with > > the recently proposed support for earlycon=efi, is likely to be useful > > to diagnose boot issues on such systems if they have no accessible serial > > port) > > > > Cc: Alexander Graf <agraf@xxxxxxx> > > Cc: Heinrich Schuchardt <xypron.glpk@xxxxxx> > > Cc: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> > > Cc: Leif Lindholm <leif.lindholm@xxxxxxxxxx> > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > > --- > > I threw this at msm8998 (arm64), and it seem to work fine as far as I > can tell. > > For what it's worth: > Tested-by: Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx> > Thanks a lot. Unless anyone has any objections, I'll get this queued up for v5.1 by the end of the week.
