Struct VmaRef

pub struct VmaRef { /* private fields */ }

A wrapper for the kernel’s struct vm_area_struct with read access.

It represents an area of virtual memory.

Invariants

The caller must hold the mmap read lock or the vma read lock.

Implementations

impl VmaRef

pub unsafe fn from_raw<'a>(vma: *const vm_area_struct) -> &'a Self

Access a virtual memory area given a raw pointer.

Safety

Callers must ensure that vma is valid for the duration of ’a, and that the mmap or vma read lock (or stronger) is held for at least the duration of ’a.

pub fn as_ptr(&self) -> *mut vm_area_struct

Returns a raw pointer to this area.

pub fn mm(&self) -> &MmWithUser

Access the underlying mm_struct.

pub fn flags(&self) -> vm_flags_t

Returns the flags associated with the virtual memory area.

The possible flags are a combination of the constants in flags.

pub fn start(&self) -> usize

Returns the (inclusive) start address of the virtual memory area.

pub fn end(&self) -> usize

Returns the (exclusive) end address of the virtual memory area.

pub fn zap_page_range_single(&self, address: usize, size: usize)

Zap pages in the given page range.

This clears page table mappings for the range at the leaf level, leaving all other page tables intact, and freeing any memory referenced by the VMA in this range. That is, anonymous memory is completely freed, file-backed memory has its reference count on page cache folio’s dropped, any dirty data will still be written back to disk as usual.

It may seem odd that we clear at the leaf level, this is however a product of the page table structure used to map physical memory into a virtual address space - each virtual address actually consists of a bitmap of array indices into page tables, which form a hierarchical page table level structure.

As a result, each page table level maps a multiple of page table levels below, and thus span ever increasing ranges of pages. At the leaf or PTE level, we map the actual physical memory.

It is here where a zap operates, as it the only place we can be certain of clearing without impacting any other virtual mappings. It is an implementation detail as to whether the kernel goes further in freeing unused page tables, but for the purposes of this operation we must only assume that the leaf level is cleared.

pub fn as_mixedmap_vma(&self) -> Option<&VmaMixedMap>

If the VM_MIXEDMAP flag is set, returns a VmaMixedMap to this VMA, otherwise returns None.

This can be used to access methods that require VM_MIXEDMAP to be set.