[PATCH] arm64: mm: Align PGDs to at least 64 bytes

[Will Deacon]

On Mon, Nov 28, 2022 at 05:50:48PM +0000, Catalin Marinas wrote:
> On Tue, Nov 22, 2022 at 05:56:18PM +0100, Ard Biesheuvel wrote:
> > My copy of the ARM ARM (DDI 0487G.a) no longer describes the 64 byte
> 
> G.a is nearly two years old. You may want to upgrade to H.a ;).

H.a is over eight months old. You may want to upgrade to I.a :p

(Actually, don't bother -- it's written using these unreadable rule things.
H.a, all is forgiven).

> > minimum alignment of root page tables as being conditional on whether
> > 52-bit physical addressing is supported and enabled, even though I seem
> > to remember that this was the case formerly (and our code suggests the
> > same).
> 
> The wording in the ARM ARM implies that it's only needed if we go beyond
> 48 bits for the base address:
> 
>   A translation table must be aligned to the size of the table, except
>   that when using a translation table base address larger than 48 bits
>   the minimum alignment of a table containing fewer than eight entries
>   is 64 bytes.

FWIW, this wording is the same in I.a.

> But I'm fine with the patch, always forcing the 64 byte alignment. With
> the 'max_t' instead of 'max' (or whatever solves Anshuman's error):
> 
> Acked-by: Catalin Marinas <catalin.marinas at arm.com>

Happy to take a v2 or add the max_t() to this version.

Will