vmm iommu: stop transiently wiring already wired pages

[kib]

Summary

vmm_iommu_modify(): split vm_iommu_map()/unmap() into separate functions

vm_iommu_map()/unmap(): stop transiently wiring already wired pages

Namely, switch from vm_fault_quick_hold() to pmap_extract() KPI to
translate gpa to hpa. Assert that the looked up hpa belongs to the wired
page, as it should be for the VM which is configured for pass-throu
(this is theoretically a restriction that could be removed on newer
DMARs).

[markj]

There are rare cases where a wired map entry might not be resident in the pmap, e.g., if someone applied mprotect(PROT_NONE) to the mapping. Here the guest vmspace is managed by vmm so we are unlikely to hit such edge cases, but it might be worth explaining in a comment why exactly we expect pmap_extract() to succeed.

[kib]

Add comment.

[jhb]

sys/amd64/vmm/vmm.c

1107

This is only used for the KASSERT AFAICT?

[kib]

Eliminate the hpa variable in vm_iommu_unmap()