From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- fs/squashfs/cache.c | 557 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 557 insertions(+) create mode 100644 fs/squashfs/cache.c (limited to 'fs/squashfs/cache.c') diff --git a/fs/squashfs/cache.c b/fs/squashfs/cache.c new file mode 100644 index 000000000..c1a83bb0e --- /dev/null +++ b/fs/squashfs/cache.c @@ -0,0 +1,557 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Squashfs - a compressed read only filesystem for Linux + * + * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 + * Phillip Lougher + * + * cache.c + */ + +/* + * Blocks in Squashfs are compressed. To avoid repeatedly decompressing + * recently accessed data Squashfs uses two small metadata and fragment caches. + * + * This file implements a generic cache implementation used for both caches, + * plus functions layered ontop of the generic cache implementation to + * access the metadata and fragment caches. + * + * To avoid out of memory and fragmentation issues with vmalloc the cache + * uses sequences of kmalloced PAGE_SIZE buffers. + * + * It should be noted that the cache is not used for file datablocks, these + * are decompressed and cached in the page-cache in the normal way. The + * cache is only used to temporarily cache fragment and metadata blocks + * which have been read as as a result of a metadata (i.e. inode or + * directory) or fragment access. Because metadata and fragments are packed + * together into blocks (to gain greater compression) the read of a particular + * piece of metadata or fragment will retrieve other metadata/fragments which + * have been packed with it, these because of locality-of-reference may be read + * in the near future. Temporarily caching them ensures they are available for + * near future access without requiring an additional read and decompress. + */ + +#include +#include +#include +#include +#include +#include +#include +#include + +#include "squashfs_fs.h" +#include "squashfs_fs_sb.h" +#include "squashfs.h" +#include "page_actor.h" + +/* + * Waiters on cache->wait_queue are keyed by the block they want, so a wakeup + * can name who it is for. A NULL key is a capacity wakeup: one entry became + * free, so wake one waiter. A block key is a publication wakeup: that block + * now has an entry, so wake every waiter which can share it. + */ +struct squashfs_cache_wait { + wait_queue_entry_t wait; + u64 block; + bool capacity_wake; +}; + +static int squashfs_cache_wake_function(wait_queue_entry_t *wait, + unsigned int mode, int sync, void *key) +{ + struct squashfs_cache_wait *cache_wait = + container_of(wait, struct squashfs_cache_wait, wait); + u64 *block = key; + + if (block && cache_wait->block != *block) + return 0; + + WRITE_ONCE(cache_wait->capacity_wake, !block); + + /* + * Wake and unlink unconditionally instead of using + * autoremove_wake_function(), which unlinks only when it changed the + * task state. A waiter can be made runnable by something which does + * not go through this queue: wake_up_process() takes TASK_NORMAL, and + * a cgroup v2 thaw calls it on every task in the cgroup, as do + * free_pid() on a pid namespace init and a late rcuwait_wake_up(). + * try_to_wake_up() then fails. Leaving such a waiter queued with a + * reason already recorded would let it act on a freed entry it was not + * given, and the failure would not consume the exclusive budget, so a + * second waiter would be woken for the same entry. + * + * list_del_init_careful() must be the last access to @cache_wait: it + * releases the waiter, whose wait structure lives on its stack, and it + * pairs with list_empty_careful() in finish_wait() to publish the + * store above. __wake_up_common() samples ->flags and the next entry + * before calling here, so it does not touch @wait afterwards either. + */ + default_wake_function(wait, mode, sync, key); + list_del_init_careful(&wait->entry); + + return 1; +} + +static void squashfs_cache_wake_block(struct squashfs_cache *cache, u64 block) +{ + /* nr_exclusive == 0: wake every waiter which matches the key. */ + __wake_up(&cache->wait_queue, TASK_NORMAL, 0, &block); +} + +/* + * Look-up block in cache, and increment usage count. If not in cache, read + * and decompress it from disk. + * + * A caller which finds no free entry sleeps on cache->wait_queue as an + * exclusive waiter, so squashfs_cache_put() releasing one entry wakes exactly + * one task. Because a wakee may find its block published in the meantime and + * share that entry rather than claim the free one, a wakee which shares hands + * its wakeup on to the next waiter. + */ +struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb, + struct squashfs_cache *cache, u64 block, int length) +{ + int i, n; + struct squashfs_cache_entry *entry; + bool capacity_wake = false; + + spin_lock(&cache->lock); + + while (1) { + bool pending, wake_next, wake_block; + + for (i = cache->curr_blk, n = 0; n < cache->entries; n++) { + if (cache->entry[i].block == block) { + cache->curr_blk = i; + break; + } + i = (i + 1) % cache->entries; + } + + if (n == cache->entries) { + /* + * Block not in cache, if all cache entries are used + * go to sleep waiting for one to become available. + */ + if (cache->unused == 0) { + struct squashfs_cache_wait wait = { + .block = block, + .capacity_wake = false, + }; + + init_wait_func(&wait.wait, + squashfs_cache_wake_function); + cache->num_waiters++; + /* + * Enqueue while still holding cache->lock, so + * that a concurrent lookup either sees us + * queued or we see the block it publishes. + */ + prepare_to_wait_exclusive(&cache->wait_queue, + &wait.wait, TASK_UNINTERRUPTIBLE); + spin_unlock(&cache->lock); + schedule(); + finish_wait(&cache->wait_queue, &wait.wait); + capacity_wake = READ_ONCE(wait.capacity_wake); + spin_lock(&cache->lock); + cache->num_waiters--; + continue; + } + + /* + * At least one unused cache entry. A simple + * round-robin strategy is used to choose the entry to + * be evicted from the cache. + */ + i = cache->next_blk; + for (n = 0; n < cache->entries; n++) { + if (cache->entry[i].refcount == 0) + break; + i = (i + 1) % cache->entries; + } + + cache->next_blk = (i + 1) % cache->entries; + entry = &cache->entry[i]; + + /* + * Initialise chosen cache entry, and fill it in from + * disk. + */ + cache->unused--; + entry->block = block; + entry->refcount = 1; + entry->pending = 1; + entry->num_waiters = 0; + entry->error = 0; + wake_block = cache->num_waiters > 0; + spin_unlock(&cache->lock); + + /* + * The entry is now findable, so release everybody + * queued for this block to share it rather than each + * waiting for an entry of their own. They will block + * on entry->wait_queue below until the read completes. + */ + if (wake_block) + squashfs_cache_wake_block(cache, block); + + entry->length = squashfs_read_data(sb, block, length, + &entry->next_index, entry->actor); + + spin_lock(&cache->lock); + + if (entry->length < 0) + entry->error = entry->length; + + entry->pending = 0; + + /* + * While filling this entry one or more other processes + * have looked it up in the cache, and have slept + * waiting for it to become available. + */ + if (entry->num_waiters) { + spin_unlock(&cache->lock); + wake_up_all(&entry->wait_queue); + } else + spin_unlock(&cache->lock); + + goto out; + } + + /* + * Block already in cache. Increment refcount so it doesn't + * get reused until we're finished with it, if it was + * previously unused there's one less cache entry available + * for reuse. + */ + entry = &cache->entry[i]; + if (entry->refcount == 0) { + cache->unused--; + /* This claims the capacity we were woken for. */ + capacity_wake = false; + } + entry->refcount++; + + /* + * If the entry is currently being filled in by another process + * go to sleep waiting for it to become available. + */ + pending = entry->pending; + if (pending) + entry->num_waiters++; + + /* + * We were woken because an entry became free, but shared a + * block instead of claiming it. Hand the wakeup on, otherwise + * the free entry sits unclaimed while others sleep. + */ + wake_next = capacity_wake && cache->unused && cache->num_waiters; + spin_unlock(&cache->lock); + + if (wake_next) + wake_up(&cache->wait_queue); + if (pending) + wait_event(entry->wait_queue, !entry->pending); + + goto out; + } + +out: + TRACE("Got %s %d, start block %lld, refcount %d, error %d\n", + cache->name, i, entry->block, entry->refcount, entry->error); + + if (entry->error) + ERROR("Unable to read %s cache entry [%llx]\n", cache->name, + block); + return entry; +} + + +/* + * Release cache entry, once usage count is zero it can be reused. + */ +void squashfs_cache_put(struct squashfs_cache_entry *entry) +{ + struct squashfs_cache *cache = entry->cache; + + spin_lock(&cache->lock); + entry->refcount--; + if (entry->refcount == 0) { + cache->unused++; + /* + * If there's any processes waiting for a block to become + * available, wake one up. + */ + if (cache->num_waiters) { + spin_unlock(&cache->lock); + wake_up(&cache->wait_queue); + return; + } + } + spin_unlock(&cache->lock); +} + +/* + * Delete cache reclaiming all kmalloced buffers. + */ +void squashfs_cache_delete(struct squashfs_cache *cache) +{ + int i, j; + + if (IS_ERR(cache) || cache == NULL) + return; + + for (i = 0; i < cache->entries; i++) { + if (cache->entry[i].data) { + for (j = 0; j < cache->pages; j++) + kfree(cache->entry[i].data[j]); + kfree(cache->entry[i].data); + } + kfree(cache->entry[i].actor); + } + + kfree(cache->entry); + kfree(cache); +} + + +/* + * Initialise cache allocating the specified number of entries, each of + * size block_size. To avoid vmalloc fragmentation issues each entry + * is allocated as a sequence of kmalloced PAGE_SIZE buffers. + */ +struct squashfs_cache *squashfs_cache_init(char *name, int entries, + int block_size) +{ + int i, j; + struct squashfs_cache *cache; + + if (entries == 0) + return NULL; + + cache = kzalloc_obj(*cache); + if (cache == NULL) { + ERROR("Failed to allocate %s cache\n", name); + return ERR_PTR(-ENOMEM); + } + + cache->entry = kzalloc_objs(*(cache->entry), entries); + if (cache->entry == NULL) { + ERROR("Failed to allocate %s cache\n", name); + goto cleanup; + } + + cache->curr_blk = 0; + cache->next_blk = 0; + cache->unused = entries; + cache->entries = entries; + cache->block_size = block_size; + cache->pages = block_size >> PAGE_SHIFT; + cache->pages = cache->pages ? cache->pages : 1; + cache->name = name; + cache->num_waiters = 0; + spin_lock_init(&cache->lock); + init_waitqueue_head(&cache->wait_queue); + + for (i = 0; i < entries; i++) { + struct squashfs_cache_entry *entry = &cache->entry[i]; + + init_waitqueue_head(&cache->entry[i].wait_queue); + entry->cache = cache; + entry->block = SQUASHFS_INVALID_BLK; + entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL); + if (entry->data == NULL) { + ERROR("Failed to allocate %s cache entry\n", name); + goto cleanup; + } + + for (j = 0; j < cache->pages; j++) { + entry->data[j] = kmalloc(PAGE_SIZE, GFP_KERNEL); + if (entry->data[j] == NULL) { + ERROR("Failed to allocate %s buffer\n", name); + goto cleanup; + } + } + + entry->actor = squashfs_page_actor_init(entry->data, + cache->pages, 0); + if (entry->actor == NULL) { + ERROR("Failed to allocate %s cache entry\n", name); + goto cleanup; + } + } + + return cache; + +cleanup: + squashfs_cache_delete(cache); + return ERR_PTR(-ENOMEM); +} + + +/* + * Copy up to length bytes from cache entry to buffer starting at offset bytes + * into the cache entry. If there's not length bytes then copy the number of + * bytes available. In all cases return the number of bytes copied. + */ +int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry, + int offset, int length) +{ + int remaining = length; + + if (length == 0 || offset < 0) + return 0; + else if (buffer == NULL) + return min(length, entry->length - offset); + + while (offset < entry->length) { + void *buff = entry->data[offset / PAGE_SIZE] + + (offset % PAGE_SIZE); + int bytes = min_t(int, entry->length - offset, + PAGE_SIZE - (offset % PAGE_SIZE)); + + if (bytes >= remaining) { + memcpy(buffer, buff, remaining); + remaining = 0; + break; + } + + memcpy(buffer, buff, bytes); + buffer += bytes; + remaining -= bytes; + offset += bytes; + } + + return length - remaining; +} + + +/* + * Read length bytes from metadata position (block is the + * start of the compressed block on disk, and offset is the offset into + * the block once decompressed). Data is packed into consecutive blocks, + * and length bytes may require reading more than one block. + */ +int squashfs_read_metadata(struct super_block *sb, void *buffer, + u64 *block, int *offset, int length) +{ + struct squashfs_sb_info *msblk = sb->s_fs_info; + int bytes, res = length; + struct squashfs_cache_entry *entry; + + TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset); + + if (unlikely(length < 0)) + return -EIO; + + if (unlikely(*offset < 0 || *offset >= SQUASHFS_METADATA_SIZE)) + return -EIO; + + while (length) { + entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0); + if (entry->error) { + res = entry->error; + goto error; + } else if (*offset >= entry->length) { + res = -EIO; + goto error; + } + + bytes = squashfs_copy_data(buffer, entry, *offset, length); + if (buffer) + buffer += bytes; + length -= bytes; + *offset += bytes; + + if (*offset == entry->length) { + *block = entry->next_index; + *offset = 0; + } + + squashfs_cache_put(entry); + } + + return res; + +error: + squashfs_cache_put(entry); + return res; +} + + +/* + * Look-up in the fragmment cache the fragment located at in the + * filesystem. If necessary read and decompress it from disk. + */ +struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb, + u64 start_block, int length) +{ + struct squashfs_sb_info *msblk = sb->s_fs_info; + + return squashfs_cache_get(sb, msblk->fragment_cache, start_block, + length); +} + + +/* + * Read and decompress the datablock located at in the + * filesystem. The cache is used here to avoid duplicating locking and + * read/decompress code. + */ +struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb, + u64 start_block, int length) +{ + struct squashfs_sb_info *msblk = sb->s_fs_info; + + return squashfs_cache_get(sb, msblk->read_page, start_block, length); +} + + +/* + * Read a filesystem table (uncompressed sequence of bytes) from disk + */ +void *squashfs_read_table(struct super_block *sb, u64 block, int length) +{ + int pages = (length + PAGE_SIZE - 1) >> PAGE_SHIFT; + int i, res; + void *table, *buffer, **data; + struct squashfs_page_actor *actor; + + table = buffer = kmalloc(length, GFP_KERNEL); + if (table == NULL) + return ERR_PTR(-ENOMEM); + + data = kcalloc(pages, sizeof(void *), GFP_KERNEL); + if (data == NULL) { + res = -ENOMEM; + goto failed; + } + + actor = squashfs_page_actor_init(data, pages, length); + if (actor == NULL) { + res = -ENOMEM; + goto failed2; + } + + for (i = 0; i < pages; i++, buffer += PAGE_SIZE) + data[i] = buffer; + + res = squashfs_read_data(sb, block, length | + SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor); + + kfree(data); + kfree(actor); + + if (res < 0) + goto failed; + + return table; + +failed2: + kfree(data); +failed: + kfree(table); + return ERR_PTR(res); +} -- cgit v1.3.1