Re: [PATCH 17/24] acpi: Ignore acpi_rsdp kernel param when the kernel has been locked down

From: Dave Young
Date: Fri Apr 07 2017 - 03:40:37 EST


On 04/07/17 at 08:05am, David Howells wrote:
> Dave Young <dyoung@xxxxxxxxxx> wrote:
>
> > > > This option allows userspace to pass the RSDP address to the kernel, which
> > > > makes it possible for a user to circumvent any restrictions imposed on
> > > > loading modules. Ignore the option when the kernel is locked down.
> > >
> > > I'm not really sure here.
> > >
> > > What exactly is the mechanism?
> >
> > Actually this acpi_rsdp param is created for EFI kexec reboot in old
> > days when we had not supported persistent efi vm space across kexec
> > reboot. At that time kexec reboot runs as noefi mode, it can not find
> > the acpi root table thus kernel will hang early.
> >
> > Now kexec can support EFI boot so this param is not necessary for most
> > user unless they still use efi=old_map.
>
> Is this patch now unnecessary?

I think it is still necessary because the acpi_rsdp kernel param is still
a valid paramater and one can still pass a pointer to be recognized as acpi
root pointer.

Maybe "imposed on loading modules" is not clear which can be dropped.

Thanks
Dave