Merge branch 'mm-enforce-ioremap-address-space-and-introduce-sparse-vm_area'

Alexei Starovoitov says:

====================
mm: Enforce ioremap address space and introduce sparse vm_area

From: Alexei Starovoitov <ast@kernel.org>

v3 -> v4
- dropped VM_XEN patch for now. It will be in the follow up.
- fixed constant as pointed out by Mike

v2 -> v3
- added Christoph's reviewed-by to patch 1
- cap commit log lines to 75 chars
- factored out common checks in patch 3 into helper
- made vm_area_unmap_pages() return void

There are various users of kernel virtual address space:
vmalloc, vmap, ioremap, xen.

- vmalloc use case dominates the usage. Such vm areas have VM_ALLOC flag
and these areas are treated differently by KASAN.

- the areas created by vmap() function should be tagged with VM_MAP
(as majority of the users do).

- ioremap areas are tagged with VM_IOREMAP and vm area start is aligned
to size of the area unlike vmalloc/vmap.

- there is also xen usage that is marked as VM_IOREMAP, but it doesn't
call ioremap_page_range() unlike all other VM_IOREMAP users.

To clean this up a bit, enforce that ioremap_page_range() checks the range
and VM_IOREMAP flag.

In addition BPF would like to reserve regions of kernel virtual address
space and populate it lazily, similar to xen use cases.
For that reason, introduce VM_SPARSE flag and vm_area_[un]map_pages()
helpers to populate this sparse area.

In the end the /proc/vmallocinfo will show
"vmalloc"
"vmap"
"ioremap"
"sparse"
categories for different kinds of address regions.

ioremap, sparse will return zero when dumped through /proc/kcore
====================

Link: https://lore.kernel.org/r/20240305030516.41519-1-alexei.starovoitov@gmail.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>