* Andy Lutomirski <l...@amacapital.net> wrote:
> On Aug 10, 2016 3:31 PM, "Ingo Molnar" <mi...@kernel.org> wrote:
> >
> >
> > One side note:
> >
> > * Andy Lutomirski <l...@kernel.org> wrote:
> >
> > > This series fixes it the other way: it allow the trampoline to live
> > > in boot services memory. It achieves this by deferring the panic
> > > due to failure to reserve a trampoline until early_initcall time
> > > and then adjusting the EFI boot services quirk to reserve space
> > > for the trampoline if we haven't already found it a home.
> >
> > > x86/efi: Allocate a trampoline if needed in efi_free_boot_services()
> >
> > Btw., this means that we first try to allocate the trampoline the old
> > fashioned
> > way, and in the rare cases this fails we allocate it from the EFI data area,
> > right?
>
> Yes, exactly.
>
> >
> > This is problematic from the probability management POV: we are creating a
> > rare
> > piece of code that will run only on a select few systems.
> >
> > I think it would be much better to allocate the trampoline from the EFI
> > area on
> > all EFI systems by default. Is there any reason why that would not work?
>
> I think most EFI systems don't have any boot services below 1MB, so
> that wouldn't work.
>
> We could try allocating from EFI more generically, but that sounds
> much scarier. The EFI memory map code is tangled with the e820 code
> and the memblock code, and I'd be nervous about confusing the e820
> code or accidentally allocating blacklisted RAM (EBDA,
> Sandybridge-quirked, etc.) The code I wrote should only allocate the
> trampoline at a different address than current kernels in cases where
> current kernels would panic.
>
> I don't like it either, but after scratching my head for a while I
> didn't come up with anything better. At least the actual special case
> is only a couple lines of code.
Ok, fine enough to me!
Matt, is patch #5:
[PATCH v2 5/5] x86/efi: Allocate a trampoline if needed in
efi_free_boot_services()
looking good to you?
Thanks,
Ingo
