Re: [PATCH V3 3/5] x86/efi: Permanently save the EFI_MEMORY_MAP passed by the firmware

[Thomas Gleixner]

On Wed, 5 Sep 2018, Ard Biesheuvel wrote:
> On 5 September 2018 at 14:56, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Wed, Sep 05, 2018 at 02:27:49PM +0200, Ard Biesheuvel wrote:
> >> Would we still need to preserve the old memory map in that case?
> >
> > I thought the reason for having this was being able to know the fault is
> > in an EFI area. But of course, I'm not wel versed in this whole EFI
> > crapola.
> 
> I'm not entirely sure whether that really matters. The EFI services
> access the stack and can access byref/pointer arguments which are not
> covered by the EFI memory map as runtime services code/data, and so
> they can trigger page faults by running off the vmapped stack or
> writing to const byref arguments.
> 
> EFI runtime services using boot services regions after they are no
> longer available are a known source of headaches, but I don't see why
> we should restrict ourselves to such cases if we bother to wire up
> fault handling specifically for EFI services calls.
> 
> So any page or permission fault occurring in the context of a EFI
> runtime services invocation should be treated the same, I think.

I agree. Keep it simple. If the EFI crap fails, then assist with the reboot
and otherwise just kill it.

Thanks,

	tglx