Re: [PATCH] x86/efi: Don't require non-blocking EFI callbacks

[Ard Biesheuvel]

On Thu, 26 Sep 2019 at 17:47, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx> wrote:
>
> On 9/26/19 4:29 PM, Ard Biesheuvel wrote:
> > On Thu, 26 Sep 2019 at 16:12, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx> wrote:
> >>
> >> If a backend does not implement non-blocking EFI operations, it implies
> >> that the normal operations are non-blocking.
> >
> > Is that documented anywhere?
>
> Sort of. From commit 6d80dba1c9fe "efi: Provide a non-blocking
> SetVariable() operation"
>
> """
> Introduce ->set_variable_nonblocking() for this use case. It is an
> optional EFI backend operation, and need only be implemented by those
> backends that usually acquire locks to serialize access to EFI
> variables, as is the case for virt_efi_set_variable() where we now grab
> the EFI runtime spinlock.
> """
>
> >
> >> Instead of crashing
> >> dereferencing a NULL pointer, fallback to the normal operations since it
> >> is safe to do so.
> >>
> >
> > I agree that crashing is never the right thing to do, but I wonder
> > whether we shouldn't just bail instead. If the provided default
> > operation is non-blocking, the platform can populate the function
> > pointer with a reference to the default implementation.
>
> If you would prefer it that platforms are always required to implement
> the non-blocking functions, then I will just send a simple patch fixing
> up the Xen implementation.
>

Yes, please, that sounds like a safer option to me.