Re: [PATCH 5/5] ArmVirtPkg: revert PcdPrePiCpuMemorySize to is default value of 48

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Fri, 23 Nov 2018 at 14:36, Andrew Jones <drjones@redhat.com> wrote:
>
> On Fri, Nov 23, 2018 at 01:14:31PM +0100, Ard Biesheuvel wrote:
> > Drop the PcdPrePiCpuMemorySize definitions that limit it to 40
> > bits on AArch64 targets. This is no longer appropriate now that
> > KVM has been enhanced to permit any IPA space size permitted by
> > the architecture. This means the value will revert back to its
> > default of 48.
>
> If we're running on older KVM, then, since KVM just passes through
> the host value of id_aa64mmfr0_el1, firmware will see whatever
> the host supports and use that (I'm not sure if the 48-bit default
> ever can come into play too). In either case, it probably doesn't
> matter, because just like the guest kernel works today on older
> KVM, as long as nothing is placed above 40 bits there isn't any
> problem. Is that the case for edk2 too?
>

The value of 48 serves as a limit now, which makes sense given that
52-bit requires 64k pages, which we don't support.

But as I said, it might make sense to permit the GCD space to describe
that much, which is actually a nice side effect of the previous patch,
which takes the value directly from the CPU system register on virt
targets.