• Alexandre Ghiti's avatar
    riscv: Allow to downgrade paging mode from the command line · 26e7aacb
    Alexandre Ghiti authored
    Add 2 early command line parameters that allow to downgrade satp mode
    (using the same naming as x86):
    - "no5lvl": use a 4-level page table (down from sv57 to sv48)
    - "no4lvl": use a 3-level page table (down from sv57/sv48 to sv39)
    
    Note that going through the device tree to get the kernel command line
    works with ACPI too since the efi stub creates a device tree anyway with
    the command line.
    
    In KASAN kernels, we can't use the libfdt that early in the boot process
    since we are not ready to execute instrumented functions. So instead of
    using the "generic" libfdt, we compile our own versions of those functions
    that are not instrumented and that are prefixed so that they do not
    conflict with the generic ones. We also need the non-instrumented versions
    of the string functions and the prefixed versions of memcpy/memmove.
    
    This is largely inspired by commit aacd149b ("arm64: head: avoid
    relocating the kernel twice for KASLR") from which I removed compilation
    flags that were not relevant to RISC-V at the moment (LTO, SCS). Also
    note that we have to link with -z norelro to avoid ld.lld to throw a
    warning with the new .got sections, like in commit 311bea3c ("arm64:
    link with -z norelro for LLD or aarch64-elf").
    Signed-off-by: default avatarAlexandre Ghiti <alexghiti@rivosinc.com>
    Tested-by: default avatarBjörn Töpel <bjorn@rivosinc.com>
    Reviewed-by: default avatarBjörn Töpel <bjorn@rivosinc.com>
    Link: https://lore.kernel.org/r/20230424092313.178699-2-alexghiti@rivosinc.comSigned-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
    26e7aacb
cmdline_early.c 1.53 KB