MFC r314310
Refine the fix from r312954. Specifically, add a new PDE-only flag,
PG_PROMOTED, that indicates whether lingering 4KB page mappings might
need to be flushed on a PDE change that restricts or destroys a 2MB
page mapping. This flag allows the pmap to avoid range invalidations
that are both unnecessary and costly.

MFC r281495:
Add config option PAE_TABLES for the i386 kernel. It switches pmap to
use PAE format for the page tables, but does not incur other
consequences of the full PAE config. In particular, vm_paddr_t and
bus_addr_t are left 32bit, and max supported memory is still limited
by 4GB.

The option allows to have nx permissions for memory mappings on i386
kernel, while keeping the usual i386 KBI and avoiding the kernel data
sizing problems typical for the PAE config.

MFC r281272:
Explain that vm_page_array is mapped to describe the memory, not the
memory itself. Provide the formula to calculate the number of
required page tables. Correct the size of the struct vm_page for
non-PAE case.

MFC r272761:
Add an argument to the x86 pmap_invalidate_cache_range() to request
forced invalidation of the cache range regardless of the presence of
self-snoop feature.

MFC r272943:
MFi386 r272761.

MFC 261781:
Don't waste a page of KVA for the boot-time memory test on x86. For amd64,
reuse the first page of the crashdumpmap as CMAP1/CADDR1. For i386,
remove CMAP1/CADDR1 entirely and reuse CMAP3/CADDR3 for the memory test.

MFC r281495:
Add config option PAE_TABLES for the i386 kernel. It switches pmap to
use PAE format for the page tables, but does not incur other
consequences of the full PAE config. In particular, vm_paddr_t and
bus_addr_t are left 32bit, and max supported memory is still limited
by 4GB.

The option allows to have nx permissions for memory mappings on i386
kernel, while keeping the usual i386 KBI and avoiding the kernel data
sizing problems typical for the PAE config.

MFC r281272:
Explain that vm_page_array is mapped to describe the memory, not the
memory itself. Provide the formula to calculate the number of
required page tables. Correct the size of the struct vm_page for
non-PAE case.

MFC r272761:
Add an argument to the x86 pmap_invalidate_cache_range() to request
forced invalidation of the cache range regardless of the presence of
self-snoop feature.

MFC r272943:
MFi386 r272761.

MFC 261781:
Don't waste a page of KVA for the boot-time memory test on x86. For amd64,
reuse the first page of the crashdumpmap as CMAP1/CADDR1. For i386,
remove CMAP1/CADDR1 entirely and reuse CMAP3/CADDR3 for the memory test.