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 r299350:
Add locking annotations to amd64 struct md_page members.

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 259641,259863,259924,259937,259961,259978,260380,260383,260410,260466,
260531,260532,260550,260619,261170,261453,261621,263280,263290,264516:
Add support for local APIC hardware-assist.
- Restructure vlapic access and register handling to support hardware-assist
for the local APIC.
- Use the 'Virtual Interrupt Delivery' and 'Posted Interrupt Processing'
feature of Intel VT-x if supported by hardware.
- Add an API to rendezvous all active vcpus in a virtual machine and use
it to support level triggered interrupts with VT-x 'Virtual Interrupt
Delivery'.
- Use a cheaper IPI handler than IPI_AST for nested page table shootdowns
and avoid doing unnecessary nested TLB invalidations.

Reviewed by: neel

MFC r263475:
Fix two issues with /dev/mem access on amd64, both causing kernel page
faults.

First, for accesses to direct map region should check for the limit by
which direct map is instantiated.

Second, for accesses to the kernel map, use a new thread private flag
TDP_DEVMEMIO, which instructs vm_fault() to return error when fault
happens on the MAP_ENTRY_NOFAULT entry, instead of panicing.

MFC r263498:
Add change forgotten in r263475. Make dmaplimit accessible outside
amd64/pmap.c.

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 259641,259863,259924,259937,259961,259978,260380,260383,260410,260466,
260531,260532,260550,260619,261170,261453,261621,263280,263290,264516:
Add support for local APIC hardware-assist.
- Restructure vlapic access and register handling to support hardware-assist
for the local APIC.
- Use the 'Virtual Interrupt Delivery' and 'Posted Interrupt Processing'
feature of Intel VT-x if supported by hardware.
- Add an API to rendezvous all active vcpus in a virtual machine and use
it to support level triggered interrupts with VT-x 'Virtual Interrupt
Delivery'.
- Use a cheaper IPI handler than IPI_AST for nested page table shootdowns
and avoid doing unnecessary nested TLB invalidations.

Reviewed by: neel

MFC r263475:
Fix two issues with /dev/mem access on amd64, both causing kernel page
faults.

First, for accesses to direct map region should check for the limit by
which direct map is instantiated.

Second, for accesses to the kernel map, use a new thread private flag
TDP_DEVMEMIO, which instructs vm_fault() to return error when fault
happens on the MAP_ENTRY_NOFAULT entry, instead of panicing.

MFC r263498:
Add change forgotten in r263475. Make dmaplimit accessible outside
amd64/pmap.c.