On Sat, 26 Jan 2019 at 16:03, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: > > On Sat, 26 Jan 2019 at 15:33, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote: > > > > On 1/26/19 1:34 PM, Alexander Graf wrote: > > > > > > > > >> 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. > > > > It think it would be helpful to add this information to the commit message. > > > > Did you read the commit message? > > > If it is strictly opt-in, I have no concern. > > > > Thanks. Below is the boot log of a EDK2 based SynQuacer UEFI/ACPI machine running with this change enabled. The dump of the memory map has been modified to show the virtual address between () https://storage.kernelci.org/ardb/for-kernelci/v5.0-rc2-3-g4f78f37fc6eb/arm64/defconfig/lab-mhart/boot-synquacer-acpi.html
