arm64 pmap: introduce PHYS_TO_PTE macro

[zachary.leaf_arm.com]

Summary

Introduce macro for PHYS_TO_PTE, setting the groundwork for future
support of various Arm VMSA extensions.

For extensions such as 52-bit VA/PA (FEAT_LPA2), the representation of
an address between a PTE and PA are not equivalent. This macro will
allow converting between the different representations.

Currently PHYS_TO_PTE is a NOP. Replace all instances where we go from
PA to PTE with new PHYS_TO_PTE macro.

Sponsored by: Arm Ltd

[kib]

I was initially confused by the macro name and no description. The purpose is to convert a physical address into the output address field of a PTE, not into PTE. At least a comment would be useful, if not a different name.

[zachary.leaf_arm.com]

• add comment

[zachary.leaf_arm.com]

In D39828#906959, @kib wrote:

I was initially confused by the macro name and no description. The purpose is to convert a physical address into the output address field of a PTE, not into PTE. At least a comment would be useful, if not a different name.

Right. This is really only the first step in creating a PTE, we still need to set all the required attribute bits etc.

It's just about changing the representation back to the input address/pte format. e.g. for FEAT_LPA2, bits 51:50 of an OA are represented by bits 9:8 of the PTE so that will need switching around.

The only alternative I can think of is PA_TO_IA(...) but not sure that's any clearer and we lose the symmetry with PTE_TO_PA; have added a comment as suggested and updated commit message.

At least for now this step is mostly about documenting places where this change of representations will need to happen.

[andrew]

In D39828#906959, @kib wrote:

I was initially confused by the macro name and no description. The purpose is to convert a physical address into the output address field of a PTE, not into PTE. At least a comment would be useful, if not a different name.

Would PA_TO_PTE_OE be better?

sys/arm64/arm64/pmap.c

2001

[kib]

In D39828#907098, @andrew wrote:

In D39828#906959, @kib wrote:

I was initially confused by the macro name and no description. The purpose is to convert a physical address into the output address field of a PTE, not into PTE. At least a comment would be useful, if not a different name.

Would PA_TO_PTE_OE be better?

What does OE mean? O is perhaps output.

[andrew]

In D39828#907117, @kib wrote:

What does OE mean? O is perhaps output.

Should be OA for Output address, the field name in the documentation.

[zachary.leaf_arm.com]

In D39828#907120, @andrew wrote:

In D39828#907117, @kib wrote:

What does OE mean? O is perhaps output.

Should be OA for Output address, the field name in the documentation.

I'm not sure it's immediately clear that the OA in PA_TO_PTE_OA refers to the PTE field name.

I find that slightly confusing since the PA *is* the OA. We're going from OA -> IA not the other way around.

[zachary.leaf_arm.com]

• rename PA_TO_PTE -> PHYS_TO_PTE for symmetry with reverse operation PTE_TO_PHYS
• pmap_kenter: remove unnecessary & ~L3_OFFSET

[andrew]

Any further issues with this change? I'd like to push with D39827.