[v3,bpf-next,0/3] mm: Cleanup and identify various users of kernel virtual address space

Message

Alexei Starovoitov Feb. 29, 2024, 11:43 p.m. UTC

From: Alexei Starovoitov <[e-mail]>

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:
1. Enforce that ioremap_page_range() checks the range and VM_IOREMAP flag
2. Introduce VM_XEN flag to separate xen us cases from ioremap

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"
"xen"
"sparse"
categories for different kinds of address regions.

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

Alexei Starovoitov (3):
  mm: Enforce VM_IOREMAP flag and range in ioremap_page_range.
  mm, xen: Separate xen use cases from ioremap.
  mm: Introduce VM_SPARSE kind and vm_area_[un]map_pages().

 arch/x86/xen/grant-table.c         |  2 +-
 drivers/xen/xenbus/xenbus_client.c |  2 +-
 include/linux/vmalloc.h            |  6 +++
 mm/vmalloc.c                       | 75 +++++++++++++++++++++++++++++-
 4 files changed, 81 insertions(+), 4 deletions(-)