• Ard Biesheuvel's avatar
    arm64: efi: Recover from synchronous exceptions occurring in firmware · 23715a26
    Ard Biesheuvel authored
    Unlike x86, which has machinery to deal with page faults that occur
    during the execution of EFI runtime services, arm64 has nothing like
    that, and a synchronous exception raised by firmware code brings down
    the whole system.
    
    With more EFI based systems appearing that were not built to run Linux
    (such as the Windows-on-ARM laptops based on Qualcomm SOCs), as well as
    the introduction of PRM (platform specific firmware routines that are
    callable just like EFI runtime services), we are more likely to run into
    issues of this sort, and it is much more likely that we can identify and
    work around such issues if they don't bring down the system entirely.
    
    Since we already use a EFI runtime services call wrapper in assembler,
    we can quite easily add some code that captures the execution state at
    the point where the call is made, allowing us to revert to this state
    and proceed execution if the call triggered a synchronous exception.
    
    Given that the kernel and the firmware don't share any data structures
    that could end up in an indeterminate state, we can happily continue
    running, as long as we mark the EFI runtime services as unavailable from
    that point on.
    Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
    Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    23715a26
fault.c 26.7 KB