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

[Ard Biesheuvel]

On Mon, 12 Oct 2026, at 14:51, Catalin Marinas wrote:
> 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).
>

Exactly. I'll send a v2.