mm: Introduce VM_SPARSE kind and vm_area_[un]map_pages().

vmap/vmalloc APIs are used to map a set of pages into contiguous kernel
virtual space.

get_vm_area() with appropriate flag is used to request an area of kernel
address range. It's used for vmalloc, vmap, ioremap, xen use cases.
- vmalloc use case dominates the usage. Such vm areas have VM_ALLOC flag.
- the areas created by vmap() function should be tagged with VM_MAP.
- ioremap areas are tagged with VM_IOREMAP.

BPF would like to extend the vmap API to implement a lazily-populated
sparse, yet contiguous kernel virtual space. Introduce VM_SPARSE flag
and vm_area_map_pages(area, start_addr, count, pages) API to map a set
of pages within a given area.
It has the same sanity checks as vmap() does.
It also checks that get_vm_area() was created with VM_SPARSE flag
which identifies such areas in /proc/vmallocinfo
and returns zero pages on read through /proc/kcore.

The next commits will introduce bpf_arena which is a sparsely populated
shared memory region between bpf program and user space process. It will
map privately-managed pages into a sparse vm area with the following steps:

  // request virtual memory region during bpf prog verification
  area = get_vm_area(area_size, VM_SPARSE);

  // on demand
  vm_area_map_pages(area, kaddr, kend, pages);
  vm_area_unmap_pages(area, kaddr, kend);

  // after bpf program is detached and unloaded
  free_vm_area(area);

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Link: https://lore.kernel.org/bpf/20240305030516.41519-3-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2024-03-04 19:05:16 -08:00 committed by Andrii Nakryiko
parent 3e49a866c9
commit e6f798225a
2 changed files with 62 additions and 2 deletions

View File

@ -35,6 +35,7 @@ struct iov_iter; /* in uio.h */
#else
#define VM_DEFER_KMEMLEAK 0
#endif
#define VM_SPARSE 0x00001000 /* sparse vm_area. not all pages are present. */
/* bits [20..32] reserved for arch specific ioremap internals */
@ -232,6 +233,10 @@ static inline bool is_vm_area_hugepages(const void *addr)
}
#ifdef CONFIG_MMU
int vm_area_map_pages(struct vm_struct *area, unsigned long start,
unsigned long end, struct page **pages);
void vm_area_unmap_pages(struct vm_struct *area, unsigned long start,
unsigned long end);
void vunmap_range(unsigned long addr, unsigned long end);
static inline void set_vm_flush_reset_perms(void *addr)
{

View File

@ -648,6 +648,58 @@ static int vmap_pages_range(unsigned long addr, unsigned long end,
return err;
}
static int check_sparse_vm_area(struct vm_struct *area, unsigned long start,
unsigned long end)
{
might_sleep();
if (WARN_ON_ONCE(area->flags & VM_FLUSH_RESET_PERMS))
return -EINVAL;
if (WARN_ON_ONCE(area->flags & VM_NO_GUARD))
return -EINVAL;
if (WARN_ON_ONCE(!(area->flags & VM_SPARSE)))
return -EINVAL;
if ((end - start) >> PAGE_SHIFT > totalram_pages())
return -E2BIG;
if (start < (unsigned long)area->addr ||
(void *)end > area->addr + get_vm_area_size(area))
return -ERANGE;
return 0;
}
/**
* vm_area_map_pages - map pages inside given sparse vm_area
* @area: vm_area
* @start: start address inside vm_area
* @end: end address inside vm_area
* @pages: pages to map (always PAGE_SIZE pages)
*/
int vm_area_map_pages(struct vm_struct *area, unsigned long start,
unsigned long end, struct page **pages)
{
int err;
err = check_sparse_vm_area(area, start, end);
if (err)
return err;
return vmap_pages_range(start, end, PAGE_KERNEL, pages, PAGE_SHIFT);
}
/**
* vm_area_unmap_pages - unmap pages inside given sparse vm_area
* @area: vm_area
* @start: start address inside vm_area
* @end: end address inside vm_area
*/
void vm_area_unmap_pages(struct vm_struct *area, unsigned long start,
unsigned long end)
{
if (check_sparse_vm_area(area, start, end))
return;
vunmap_range(start, end);
}
int is_vmalloc_or_module_addr(const void *x)
{
/*
@ -3822,9 +3874,9 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
if (flags & VMAP_RAM)
copied = vmap_ram_vread_iter(iter, addr, n, flags);
else if (!(vm && (vm->flags & VM_IOREMAP)))
else if (!(vm && (vm->flags & (VM_IOREMAP | VM_SPARSE))))
copied = aligned_vread_iter(iter, addr, n);
else /* IOREMAP area is treated as memory hole */
else /* IOREMAP | SPARSE area is treated as memory hole */
copied = zero_iter(iter, n);
addr += copied;
@ -4415,6 +4467,9 @@ static int s_show(struct seq_file *m, void *p)
if (v->flags & VM_IOREMAP)
seq_puts(m, " ioremap");
if (v->flags & VM_SPARSE)
seq_puts(m, " sparse");
if (v->flags & VM_ALLOC)
seq_puts(m, " vmalloc");