[RFC PATCH v2 15/26] of/fdt: Introduce early_init_dt_add_memory_hyp()

[Rob Herring]

On Tue, Jan 12, 2021 at 3:51 AM Quentin Perret <qperret at google.com> wrote:
>
> On Monday 11 Jan 2021 at 08:45:10 (-0600), Rob Herring wrote:
> > On Fri, Jan 8, 2021 at 6:16 AM Quentin Perret <qperret at google.com> wrote:
> > >
> > > Introduce early_init_dt_add_memory_hyp() to allow KVM to conserve a copy
> > > of the memory regions parsed from DT. This will be needed in the context
> > > of the protected nVHE feature of KVM/arm64 where the code running at EL2
> > > will be cleanly separated from the host kernel during boot, and will
> > > need its own representation of memory.
> >
> > What happened to doing this with memblock?
>
> I gave it a go, but as mentioned in v1, I ran into issues for nomap
> regions. I want the hypervisor to know about these memory regions (it's
> possible some of those will be given to protected guests for instance)
> but these seem to be entirely removed from the memblocks when using DT:
>
> https://elixir.bootlin.com/linux/latest/source/drivers/of/fdt.c#L1153
>
> EFI appears to do things differently, though, as it 'just' uses
> memblock_mark_nomap() instead of actively removing the memblock. And that
> means I could actually use the memblock API for EFI, but I'd rather
> have a common solution. I tried to understand why things are done
> differently but couldn't find an answer and kept things simple and
> working for now.
>
> Is there a good reason for not using memblock_mark_nomap() with DT? If
> not, I'm happy to try that.

There were 2 patches to do that, but it never got resolved. See here[1].

Rob

[1] https://lore.kernel.org/linux-devicetree/?q=s%3Ano-map