include/linux/hmm.h

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Copyright 2013 Red Hat Inc.
 *
 * Authors: Jérôme Glisse <jglisse@redhat.com>
 *
 * 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 {
	/* Output fields and flags */
	HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
	HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
	HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
	HMM_PFN_ORDER_SHIFT = (BITS_PER_LONG - 8),

	/* Input flags */
	HMM_PFN_REQ_FAULT = HMM_PFN_VALID,
	HMM_PFN_REQ_WRITE = HMM_PFN_WRITE,

	HMM_PFN_FLAGS = 0xFFUL << HMM_PFN_ORDER_SHIFT,
};

/*
 * 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)
{
	return pfn_to_page(hmm_pfn & ~HMM_PFN_FLAGS);
}

/*
 * 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)
{
	return (hmm_pfn >> HMM_PFN_ORDER_SHIFT) & 0x1F;
}

/*
 * 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 {
	struct mmu_interval_notifier *notifier;
	unsigned long		notifier_seq;
	unsigned long		start;
	unsigned long		end;
	unsigned long		*hmm_pfns;
	unsigned long		default_flags;
	unsigned long		pfn_flags_mask;
	void			*dev_private_owner;
};

/*
 * 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 1000

#endif /* LINUX_HMM_H */