On Sat, 26 Jan 2019, 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> Tested-by: Lee Jones <lee.jones@xxxxxxxxxx> -- Lee Jones [李琼斯] Linaro Services Technical Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog
