vm: pair up conversion macros

[dougm]

Summary

In the vm domain, where a pair of macros are frequently composed, with inner macro transforming one type to another and then the outer macro transforming that to a third type, define some macros to combine the transformations and allow shorter lines that use them.

Specifically, define VM_PAGE_TO_DMAP and DMAP_TO_VM_PAGE to transform back and forth via the intermediate type PHYS, and use the new macros everywhere they apply. For riscv and arm64 specifically, define PTE_TO_DMAP to compose a pair of transformations via PHYS, and use them where feasible.

Test Plan

Kernels for i386, amd64, powerpc, riscv and arm64 have been compiled successfully.

[bz]

sys/compat/linuxkpi/common/src/linux_page.c

207

@markj seems this was added after my initial PAGE_IS_LKPI_PAGE pass.
@dougm can we leave the temp variable please as in the future linux_free_pages may accept a real struct page and not a vm_page_t

[mhorne]

sys/amd64/acpica/acpi_wakeup.c

348

Passing the type as an argument is not a win for readability, IMO. I suggest simply casting where needed, as the resulting line length is the same.

[dougm]

Make changes to address feedback.

[markj]

sys/amd64/acpica/acpi_wakeup.c

348

To be honest, I don't really like this ASSIGN_VM_PAGE_TO_DMAP. It's a strange syntax for assigning to a local variable. It looks as though it's performing some kind of global operation under the hood.

[jhibbits]

sys/vm/vm.h

61

If you're trying to simply avoid casting, why not make this new VM_PAGE_TO_DMAP() return a (void *)?