> Am 26.01.2019 um 13:28 schrieb Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>: > >> On Sat, 26 Jan 2019 at 13:27, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote: >> >>> On 1/26/19 11:22 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) >>> >> >> NAK >> > > Excuse me? > >> This patch breaks EFI booting with any known U-Boot release. >> > > It does if you pass 'efi=novmap'. Otherwise, it works fine. Even then it doesn't break the entire boot, only runtime services (which are guarded anyway). I would claim that in most cases, we do not break even. Alex
