Re: [PATCH] arm64/mm: Route faults taken by EFI runtime firmware to no_context

[Catalin Marinas <catalin.marinas@arm.com>]

On Mon, Oct 12, 2026 at 10:36:41AM +0200, Ard Biesheuvel wrote:
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index 0b52557652be..db308fe01c4f 100644
> > --- a/arch/arm64/mm/fault.c
> > +++ b/arch/arm64/mm/fault.c
> > @@ -40,6 +40,7 @@
> >  #include <asm/kprobes.h>
> >  #include <asm/mte.h>
> >  #include <asm/processor.h>
> > +#include <asm/stacktrace.h>
> >  #include <asm/sysreg.h>
> >  #include <asm/system_misc.h>
> >  #include <asm/tlbflush.h>
> > @@ -621,6 +622,17 @@ static int __kprobes do_page_fault(unsigned long 
> > far, unsigned long esr,
> >  	if (faulthandler_disabled() || !mm)
> >  		goto no_context;
> > 
> > +	/*
> > +	 * Faults taken by EFI runtime services firmware are never resolved by
> > +	 * the mm (efi_mm has no VMAs), and must reach __do_kernel_fault() so
> > +	 * that efi_runtime_fixup_exception() can recover from them. When EFI
> > +	 * runtime services are invoked from a preemptible kthread, neither of
> > +	 * the conditions above applies, so check for this explicitly.
> > +	 */
> > +	if (IS_ENABLED(CONFIG_EFI) && !user_mode(regs) &&
> > +	    is_ttbr0_addr(regs->pc) && current_in_efi())
> > +		goto no_context;
> > +
> 
> Looking at this again, I wonder if we should just add a comparison with
> &efi_mm to the preceding if() condition.

I think mm_is_efi() check in the previous block is simpler. I couldn't
find any case where this wouldn't cover the more extensive check above
(or the other way around).

-- 
Catalin