[PATCH] arm64: efi: Recover from synchronous exceptions occurring in firmware

[Catalin Marinas]

On Wed, Nov 02, 2022 at 10:08:28AM +0100, Ard Biesheuvel wrote:
> On Fri, 28 Oct 2022 at 17:01, Ard Biesheuvel <ardb at kernel.org> wrote:
> >
> > 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: Ard Biesheuvel <ardb at kernel.org>
> 
> Does anyone mind if I take this via the EFI tree for v6.1?

No, feel free to take it.

Acked-by: Catalin Marinas <catalin.marinas at arm.com>