[PATCH v1 10/12] KVM: arm64: Rework logic to en/decode VTCR_EL2.{SL0, SL2} fields

[Oliver Upton]

Hi Ryan,

On Tue, Dec 06, 2022 at 01:59:28PM +0000, Ryan Roberts wrote:
> In order to support 5 level translation, FEAT_LPA2 introduces the 1-bit
> SL2 field within VTCR_EL2 to extend the existing 2-bit SL0 field. The
> SL2[0]:SL0[1:0] encodings have no simple algorithmic relationship to the
> start levels they represent (that I can find, at least), so replace the
> existing macros with functions that do lookups to encode and decode the
> values. These new functions no longer make hardcoded assumptions about
> the maximum level and instead rely on KVM_PGTABLE_FIRST_LEVEL and
> KVM_PGTABLE_LAST_LEVEL.
> 
> This is preparatory work for enabling 52-bit IPA for 4KB and 16KB pages
> with FEAT_LPA2.
> 
> No functional change intended.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts at arm.com>

Why do we need to support 5-level paging at stage-2?

A configuration of start_level = 0, T0SZ = 12 with 4K paging would
result in 16 concatenated tables at level 0, avoiding the level -1
lookup altogether.

--
Thanks,
Oliver