cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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frontswap.c (8056B)


      1// SPDX-License-Identifier: GPL-2.0-only
      2/*
      3 * Frontswap frontend
      4 *
      5 * This code provides the generic "frontend" layer to call a matching
      6 * "backend" driver implementation of frontswap.  See
      7 * Documentation/vm/frontswap.rst for more information.
      8 *
      9 * Copyright (C) 2009-2012 Oracle Corp.  All rights reserved.
     10 * Author: Dan Magenheimer
     11 */
     12
     13#include <linux/mman.h>
     14#include <linux/swap.h>
     15#include <linux/swapops.h>
     16#include <linux/security.h>
     17#include <linux/module.h>
     18#include <linux/debugfs.h>
     19#include <linux/frontswap.h>
     20#include <linux/swapfile.h>
     21
     22DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
     23
     24/*
     25 * frontswap_ops are added by frontswap_register_ops, and provide the
     26 * frontswap "backend" implementation functions.  Multiple implementations
     27 * may be registered, but implementations can never deregister.  This
     28 * is a simple singly-linked list of all registered implementations.
     29 */
     30static const struct frontswap_ops *frontswap_ops __read_mostly;
     31
     32#ifdef CONFIG_DEBUG_FS
     33/*
     34 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
     35 * properly configured).  These are for information only so are not protected
     36 * against increment races.
     37 */
     38static u64 frontswap_loads;
     39static u64 frontswap_succ_stores;
     40static u64 frontswap_failed_stores;
     41static u64 frontswap_invalidates;
     42
     43static inline void inc_frontswap_loads(void)
     44{
     45	data_race(frontswap_loads++);
     46}
     47static inline void inc_frontswap_succ_stores(void)
     48{
     49	data_race(frontswap_succ_stores++);
     50}
     51static inline void inc_frontswap_failed_stores(void)
     52{
     53	data_race(frontswap_failed_stores++);
     54}
     55static inline void inc_frontswap_invalidates(void)
     56{
     57	data_race(frontswap_invalidates++);
     58}
     59#else
     60static inline void inc_frontswap_loads(void) { }
     61static inline void inc_frontswap_succ_stores(void) { }
     62static inline void inc_frontswap_failed_stores(void) { }
     63static inline void inc_frontswap_invalidates(void) { }
     64#endif
     65
     66/*
     67 * Due to the asynchronous nature of the backends loading potentially
     68 * _after_ the swap system has been activated, we have chokepoints
     69 * on all frontswap functions to not call the backend until the backend
     70 * has registered.
     71 *
     72 * This would not guards us against the user deciding to call swapoff right as
     73 * we are calling the backend to initialize (so swapon is in action).
     74 * Fortunately for us, the swapon_mutex has been taken by the callee so we are
     75 * OK. The other scenario where calls to frontswap_store (called via
     76 * swap_writepage) is racing with frontswap_invalidate_area (called via
     77 * swapoff) is again guarded by the swap subsystem.
     78 *
     79 * While no backend is registered all calls to frontswap_[store|load|
     80 * invalidate_area|invalidate_page] are ignored or fail.
     81 *
     82 * The time between the backend being registered and the swap file system
     83 * calling the backend (via the frontswap_* functions) is indeterminate as
     84 * frontswap_ops is not atomic_t (or a value guarded by a spinlock).
     85 * That is OK as we are comfortable missing some of these calls to the newly
     86 * registered backend.
     87 *
     88 * Obviously the opposite (unloading the backend) must be done after all
     89 * the frontswap_[store|load|invalidate_area|invalidate_page] start
     90 * ignoring or failing the requests.  However, there is currently no way
     91 * to unload a backend once it is registered.
     92 */
     93
     94/*
     95 * Register operations for frontswap
     96 */
     97int frontswap_register_ops(const struct frontswap_ops *ops)
     98{
     99	if (frontswap_ops)
    100		return -EINVAL;
    101
    102	frontswap_ops = ops;
    103	static_branch_inc(&frontswap_enabled_key);
    104	return 0;
    105}
    106
    107/*
    108 * Called when a swap device is swapon'd.
    109 */
    110void frontswap_init(unsigned type, unsigned long *map)
    111{
    112	struct swap_info_struct *sis = swap_info[type];
    113
    114	VM_BUG_ON(sis == NULL);
    115
    116	/*
    117	 * p->frontswap is a bitmap that we MUST have to figure out which page
    118	 * has gone in frontswap. Without it there is no point of continuing.
    119	 */
    120	if (WARN_ON(!map))
    121		return;
    122	/*
    123	 * Irregardless of whether the frontswap backend has been loaded
    124	 * before this function or it will be later, we _MUST_ have the
    125	 * p->frontswap set to something valid to work properly.
    126	 */
    127	frontswap_map_set(sis, map);
    128	frontswap_ops->init(type);
    129}
    130
    131static bool __frontswap_test(struct swap_info_struct *sis,
    132				pgoff_t offset)
    133{
    134	if (sis->frontswap_map)
    135		return test_bit(offset, sis->frontswap_map);
    136	return false;
    137}
    138
    139static inline void __frontswap_set(struct swap_info_struct *sis,
    140				   pgoff_t offset)
    141{
    142	set_bit(offset, sis->frontswap_map);
    143	atomic_inc(&sis->frontswap_pages);
    144}
    145
    146static inline void __frontswap_clear(struct swap_info_struct *sis,
    147				     pgoff_t offset)
    148{
    149	clear_bit(offset, sis->frontswap_map);
    150	atomic_dec(&sis->frontswap_pages);
    151}
    152
    153/*
    154 * "Store" data from a page to frontswap and associate it with the page's
    155 * swaptype and offset.  Page must be locked and in the swap cache.
    156 * If frontswap already contains a page with matching swaptype and
    157 * offset, the frontswap implementation may either overwrite the data and
    158 * return success or invalidate the page from frontswap and return failure.
    159 */
    160int __frontswap_store(struct page *page)
    161{
    162	int ret = -1;
    163	swp_entry_t entry = { .val = page_private(page), };
    164	int type = swp_type(entry);
    165	struct swap_info_struct *sis = swap_info[type];
    166	pgoff_t offset = swp_offset(entry);
    167
    168	VM_BUG_ON(!frontswap_ops);
    169	VM_BUG_ON(!PageLocked(page));
    170	VM_BUG_ON(sis == NULL);
    171
    172	/*
    173	 * If a dup, we must remove the old page first; we can't leave the
    174	 * old page no matter if the store of the new page succeeds or fails,
    175	 * and we can't rely on the new page replacing the old page as we may
    176	 * not store to the same implementation that contains the old page.
    177	 */
    178	if (__frontswap_test(sis, offset)) {
    179		__frontswap_clear(sis, offset);
    180		frontswap_ops->invalidate_page(type, offset);
    181	}
    182
    183	ret = frontswap_ops->store(type, offset, page);
    184	if (ret == 0) {
    185		__frontswap_set(sis, offset);
    186		inc_frontswap_succ_stores();
    187	} else {
    188		inc_frontswap_failed_stores();
    189	}
    190
    191	return ret;
    192}
    193
    194/*
    195 * "Get" data from frontswap associated with swaptype and offset that were
    196 * specified when the data was put to frontswap and use it to fill the
    197 * specified page with data. Page must be locked and in the swap cache.
    198 */
    199int __frontswap_load(struct page *page)
    200{
    201	int ret = -1;
    202	swp_entry_t entry = { .val = page_private(page), };
    203	int type = swp_type(entry);
    204	struct swap_info_struct *sis = swap_info[type];
    205	pgoff_t offset = swp_offset(entry);
    206
    207	VM_BUG_ON(!frontswap_ops);
    208	VM_BUG_ON(!PageLocked(page));
    209	VM_BUG_ON(sis == NULL);
    210
    211	if (!__frontswap_test(sis, offset))
    212		return -1;
    213
    214	/* Try loading from each implementation, until one succeeds. */
    215	ret = frontswap_ops->load(type, offset, page);
    216	if (ret == 0)
    217		inc_frontswap_loads();
    218	return ret;
    219}
    220
    221/*
    222 * Invalidate any data from frontswap associated with the specified swaptype
    223 * and offset so that a subsequent "get" will fail.
    224 */
    225void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
    226{
    227	struct swap_info_struct *sis = swap_info[type];
    228
    229	VM_BUG_ON(!frontswap_ops);
    230	VM_BUG_ON(sis == NULL);
    231
    232	if (!__frontswap_test(sis, offset))
    233		return;
    234
    235	frontswap_ops->invalidate_page(type, offset);
    236	__frontswap_clear(sis, offset);
    237	inc_frontswap_invalidates();
    238}
    239
    240/*
    241 * Invalidate all data from frontswap associated with all offsets for the
    242 * specified swaptype.
    243 */
    244void __frontswap_invalidate_area(unsigned type)
    245{
    246	struct swap_info_struct *sis = swap_info[type];
    247
    248	VM_BUG_ON(!frontswap_ops);
    249	VM_BUG_ON(sis == NULL);
    250
    251	if (sis->frontswap_map == NULL)
    252		return;
    253
    254	frontswap_ops->invalidate_area(type);
    255	atomic_set(&sis->frontswap_pages, 0);
    256	bitmap_zero(sis->frontswap_map, sis->max);
    257}
    258
    259static int __init init_frontswap(void)
    260{
    261#ifdef CONFIG_DEBUG_FS
    262	struct dentry *root = debugfs_create_dir("frontswap", NULL);
    263	if (root == NULL)
    264		return -ENXIO;
    265	debugfs_create_u64("loads", 0444, root, &frontswap_loads);
    266	debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_stores);
    267	debugfs_create_u64("failed_stores", 0444, root,
    268			   &frontswap_failed_stores);
    269	debugfs_create_u64("invalidates", 0444, root, &frontswap_invalidates);
    270#endif
    271	return 0;
    272}
    273
    274module_init(init_frontswap);