linux/include/linux/hmm.h

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Copyright 2013 Red Hat Inc.
 *
 * Authors: Jérôme Glisse <[email protected]>
 *
 * See Documentation/mm/hmm.rst for reasons and overview of what HMM is.
 */
#ifndef LINUX_HMM_H
#define LINUX_HMM_H

#include <linux/mm.h>

struct mmu_interval_notifier;

/*
 * On output:
 * 0             - The page is faultable and a future call with 
 *                 HMM_PFN_REQ_FAULT could succeed.
 * HMM_PFN_VALID - the pfn field points to a valid PFN. This PFN is at
 *                 least readable. If dev_private_owner is !NULL then this could
 *                 point at a DEVICE_PRIVATE page.
 * HMM_PFN_WRITE - if the page memory can be written to (requires HMM_PFN_VALID)
 * HMM_PFN_ERROR - accessing the pfn is impossible and the device should
 *                 fail. ie poisoned memory, special pages, no vma, etc
 *
 * On input:
 * 0                 - Return the current state of the page, do not fault it.
 * HMM_PFN_REQ_FAULT - The output must have HMM_PFN_VALID or hmm_range_fault()
 *                     will fail
 * HMM_PFN_REQ_WRITE - The output must have HMM_PFN_WRITE or hmm_range_fault()
 *                     will fail. Must be combined with HMM_PFN_REQ_FAULT.
 */
enum hmm_pfn_flags { … };

/*
 * hmm_pfn_to_page() - return struct page pointed to by a device entry
 *
 * This must be called under the caller 'user_lock' after a successful
 * mmu_interval_read_begin(). The caller must have tested for HMM_PFN_VALID
 * already.
 */
static inline struct page *hmm_pfn_to_page(unsigned long hmm_pfn)
{ … }

/*
 * hmm_pfn_to_map_order() - return the CPU mapping size order
 *
 * This is optionally useful to optimize processing of the pfn result
 * array. It indicates that the page starts at the order aligned VA and is
 * 1<<order bytes long.  Every pfn within an high order page will have the
 * same pfn flags, both access protections and the map_order.  The caller must
 * be careful with edge cases as the start and end VA of the given page may
 * extend past the range used with hmm_range_fault().
 *
 * This must be called under the caller 'user_lock' after a successful
 * mmu_interval_read_begin(). The caller must have tested for HMM_PFN_VALID
 * already.
 */
static inline unsigned int hmm_pfn_to_map_order(unsigned long hmm_pfn)
{ … }

/*
 * struct hmm_range - track invalidation lock on virtual address range
 *
 * @notifier: a mmu_interval_notifier that includes the start/end
 * @notifier_seq: result of mmu_interval_read_begin()
 * @start: range virtual start address (inclusive)
 * @end: range virtual end address (exclusive)
 * @hmm_pfns: array of pfns (big enough for the range)
 * @default_flags: default flags for the range (write, read, ... see hmm doc)
 * @pfn_flags_mask: allows to mask pfn flags so that only default_flags matter
 * @dev_private_owner: owner of device private pages
 */
struct hmm_range { … };

/*
 * Please see Documentation/mm/hmm.rst for how to use the range API.
 */
int hmm_range_fault(struct hmm_range *range);

/*
 * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range
 *
 * When waiting for mmu notifiers we need some kind of time out otherwise we
 * could potentially wait for ever, 1000ms ie 1s sounds like a long time to
 * wait already.
 */
#define HMM_RANGE_DEFAULT_TIMEOUT …

#endif /* LINUX_HMM_H */