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// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
module userspace_swap.mojom;
struct MemoryRegion {
uint64 address;
uint64 length;
};
// The UserspaceSwapInitialization interface is used for the renderer to
// negotiate userspace swap with the browser.
interface UserspaceSwapInitialization {
// TransferUserfaultFD is called from the renderer to hand over the
// userfaultfd it created or to provide an error for why a userfaultfd
// could not be created. |swap_area| is a memory region which was created
// with PROT_NONE at a random address which can be used as a destination
// for MovePtes.
[Sync]
TransferUserfaultFD(uint64 uffd_error, handle<platform> uffd_handle,
uint64 mmap_error, MemoryRegion swap_area) => ();
};
// The UserspaceSwap interface are the messages the browser will send to a
// renderer to prepare for and complete userspace swap.
interface UserspaceSwap {
// The MovePTEsLeavingMapping message tells the renderer to move the
// region located at the region |src| to |dest|. The renderer
// will move the page table entries leaving the source |address| mapped.
//
// CAUTION: There is an inherent race condition that exists when using
// this message. It's entirely possible that a mapping may be unmapped
// and an unrelated one remapped at this same address. This situation
// which can be detected (by use of userfaultfd) cannot be avoided. The
// expectation is that this message will only be used on mappings which
// should never be unmapped. As a result detected unmaps or failures
// to perform the remap will result in the receiver of this message
// being killed.
MovePTEsLeavingMapping(MemoryRegion src, uint64 dest);
// The MapArea message tells the renderer to mmap an area as PROT_NONE.
// The primary use of this is to cause memory to be dropped without being
// recounted. It's possible to use MADV_DONTNEED to accomplish the same;
// however, that's less than ideal as it not reset the VMA itself. When
// using MMAP_FIXED the result is unmapping what is at that location
// first while holding the mm semaphore in write mode. This mapping will
// be created (MAP_ANONYMOUS | MAP_FIXED) with PROT_NONE protections.
//
// Ultimately we need to discard the remapped memory, unregister with
// userfaultfd, and mark a region as PROT_NONE so it can be merged
// with it's neighboring previously split VMAs. A single mmap(2)
// can accomplish all of these things.
MapArea(MemoryRegion area);
// GetPartitionAllocAreasUsed will return ranges of memory which are in
// use and also in core. The memory will be tested using mincore(2) before
// being included. |max_superpages| can be used to limited the number of
// items returned.
GetPartitionAllocSuperPagesUsed(int32 max_superpages)
=> (array<MemoryRegion> superpages);
};
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