KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

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 <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 262 insertions, 0 deletions

diff --git a/fs/afs/callback.c b/fs/afs/callback.c
new file mode 100644
index 000000000..61354003c
--- /dev/null
+++ b/fs/afs/callback.c
@@ -0,0 +1,262 @@
+/*
+ * Copyright (c) 2002, 2007 Red Hat, Inc. All rights reserved.
+ *
+ * This software may be freely redistributed under the terms of the
+ * GNU General Public License.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * Authors: David Woodhouse <dwmw2@infradead.org>
+ *          David Howells <dhowells@redhat.com>
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/circ_buf.h>
+#include <linux/sched.h>
+#include "internal.h"
+
+/*
+ * Handle invalidation of an mmap'd file.  We invalidate all the PTEs referring
+ * to the pages in this file's pagecache, forcing the kernel to go through
+ * ->fault() or ->page_mkwrite() - at which point we can handle invalidation
+ * more fully.
+ */
+void afs_invalidate_mmap_work(struct work_struct *work)
+{
+	struct afs_vnode *vnode = container_of(work, struct afs_vnode, cb_work);
+
+	unmap_mapping_pages(vnode->netfs.inode.i_mapping, 0, 0, false);
+}
+
+static void afs_volume_init_callback(struct afs_volume *volume)
+{
+	struct afs_vnode *vnode;
+
+	down_read(&volume->open_mmaps_lock);
+
+	list_for_each_entry(vnode, &volume->open_mmaps, cb_mmap_link) {
+		if (vnode->cb_v_check != atomic_read(&volume->cb_v_break)) {
+			afs_clear_cb_promise(vnode, afs_cb_promise_clear_vol_init_cb);
+			queue_work(system_dfl_wq, &vnode->cb_work);
+		}
+	}
+
+	up_read(&volume->open_mmaps_lock);
+}
+
+/*
+ * Allow the fileserver to request callback state (re-)initialisation.
+ * Unfortunately, UUIDs are not guaranteed unique.
+ */
+void afs_init_callback_state(struct afs_server *server)
+{
+	struct afs_server_entry *se;
+
+	down_read(&server->cell->vs_lock);
+
+	list_for_each_entry(se, &server->volumes, slink) {
+		se->cb_expires_at = AFS_NO_CB_PROMISE;
+		se->volume->cb_expires_at = AFS_NO_CB_PROMISE;
+		trace_afs_cb_v_break(se->volume->vid, atomic_read(&se->volume->cb_v_break),
+				     afs_cb_break_for_s_reinit);
+		if (!list_empty(&se->volume->open_mmaps))
+			afs_volume_init_callback(se->volume);
+	}
+
+	up_read(&server->cell->vs_lock);
+}
+
+/*
+ * actually break a callback
+ */
+void __afs_break_callback(struct afs_vnode *vnode, enum afs_cb_break_reason reason)
+{
+	_enter("");
+
+	clear_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags);
+	if (afs_clear_cb_promise(vnode, afs_cb_promise_clear_cb_break)) {
+		vnode->cb_break++;
+		vnode->cb_v_check = atomic_read(&vnode->volume->cb_v_break);
+		afs_clear_permits(vnode);
+
+		if (vnode->lock_state == AFS_VNODE_LOCK_WAITING_FOR_CB)
+			afs_lock_may_be_available(vnode);
+
+		if (reason != afs_cb_break_for_deleted &&
+		    vnode->status.type == AFS_FTYPE_FILE &&
+		    atomic_read(&vnode->cb_nr_mmap))
+			queue_work(system_dfl_wq, &vnode->cb_work);
+
+		trace_afs_cb_break(&vnode->fid, vnode->cb_break, reason, true);
+	} else {
+		trace_afs_cb_break(&vnode->fid, vnode->cb_break, reason, false);
+	}
+}
+
+void afs_break_callback(struct afs_vnode *vnode, enum afs_cb_break_reason reason)
+{
+	write_seqlock(&vnode->cb_lock);
+	__afs_break_callback(vnode, reason);
+	write_sequnlock(&vnode->cb_lock);
+}
+
+/*
+ * Look up a volume by volume ID under RCU conditions.
+ */
+static struct afs_volume *afs_lookup_volume_rcu(struct afs_cell *cell,
+						afs_volid_t vid)
+{
+	struct afs_volume *volume = NULL;
+	struct rb_node *p;
+
+	scoped_seqlock_read(&cell->volume_lock, ss_lock) {
+		/* Unfortunately, rbtree walking doesn't give reliable results
+		 * under just the RCU read lock, so we have to check for
+		 * changes.
+		 */
+		p = rcu_dereference_raw(cell->volumes.rb_node);
+		while (p) {
+			volume = rb_entry(p, struct afs_volume, cell_node);
+
+			if (volume->vid < vid)
+				p = rcu_dereference_raw(p->rb_left);
+			else if (volume->vid > vid)
+				p = rcu_dereference_raw(p->rb_right);
+			else
+				break;
+			volume = NULL;
+		}
+
+		if (volume && afs_try_get_volume(volume, afs_volume_trace_get_callback))
+			break;
+		volume = NULL;
+	}
+
+	return volume;
+}
+
+/*
+ * Allow the fileserver to break callbacks at the volume-level.  This is
+ * typically done when, for example, a R/W volume is snapshotted to a R/O
+ * volume (the only way to change an R/O volume).  It may also, however, happen
+ * when a volserver takes control of a volume (offlining it, moving it, etc.).
+ *
+ * Every file in that volume will need to be reevaluated.
+ */
+static void afs_break_volume_callback(struct afs_server *server,
+				      struct afs_volume *volume)
+	__releases(RCU)
+{
+	struct afs_server_list *slist = rcu_dereference(volume->servers);
+	unsigned int i, cb_v_break;
+
+	write_lock(&volume->cb_v_break_lock);
+
+	for (i = 0; i < slist->nr_servers; i++)
+		if (slist->servers[i].server == server)
+			slist->servers[i].cb_expires_at = AFS_NO_CB_PROMISE;
+	volume->cb_expires_at = AFS_NO_CB_PROMISE;
+
+	cb_v_break = atomic_inc_return_release(&volume->cb_v_break);
+	trace_afs_cb_v_break(volume->vid, cb_v_break, afs_cb_break_for_volume_callback);
+
+	write_unlock(&volume->cb_v_break_lock);
+	rcu_read_unlock();
+
+	if (!list_empty(&volume->open_mmaps))
+		afs_volume_init_callback(volume);
+}
+
+/*
+ * allow the fileserver to explicitly break one callback
+ * - happens when
+ *   - the backing file is changed
+ *   - a lock is released
+ */
+static void afs_break_one_callback(struct afs_server *server,
+				   struct afs_volume *volume,
+				   struct afs_fid *fid)
+{
+	struct super_block *sb;
+	struct afs_vnode *vnode;
+	struct inode *inode;
+
+	/* See if we can find a matching inode - even an I_NEW inode needs to
+	 * be marked as it can have its callback broken before we finish
+	 * setting up the local inode.
+	 */
+	sb = rcu_dereference(volume->sb);
+	if (!sb)
+		return;
+
+	inode = find_inode_rcu(sb, fid->vnode, afs_ilookup5_test_by_fid, fid);
+	if (inode) {
+		vnode = AFS_FS_I(inode);
+		afs_break_callback(vnode, afs_cb_break_for_callback);
+	} else {
+		trace_afs_cb_miss(fid, afs_cb_break_for_callback);
+	}
+}
+
+static void afs_break_some_callbacks(struct afs_server *server,
+				     struct afs_callback_break *cbb,
+				     size_t *_count)
+{
+	struct afs_callback_break *residue = cbb;
+	struct afs_volume *volume;
+	afs_volid_t vid = cbb->fid.vid;
+	size_t i;
+
+	rcu_read_lock();
+	volume = afs_lookup_volume_rcu(server->cell, vid);
+	if (!volume) {
+		/* Ignore breaks on unknown volumes. */
+		rcu_read_unlock();
+		*_count = 0;
+	} else if (cbb->fid.vnode == 0 && cbb->fid.unique == 0) {
+		afs_break_volume_callback(server, volume);
+		*_count -= 1;
+		if (*_count)
+			memmove(cbb, cbb + 1, sizeof(*cbb) * *_count);
+	} else {
+		/* TODO: Find all matching volumes if we couldn't match the server and
+		 * break them anyway.
+		 */
+
+		for (i = *_count; i > 0; cbb++, i--) {
+			if (cbb->fid.vid == vid) {
+				_debug("- Fid { vl=%08llx n=%llu u=%u }",
+				       cbb->fid.vid,
+				       cbb->fid.vnode,
+				       cbb->fid.unique);
+				--*_count;
+				if (volume)
+					afs_break_one_callback(server, volume, &cbb->fid);
+			} else {
+				*residue++ = *cbb;
+			}
+		}
+		rcu_read_unlock();
+	}
+
+	afs_put_volume(volume, afs_volume_trace_put_callback);
+}
+
+/*
+ * allow the fileserver to break callback promises
+ */
+void afs_break_callbacks(struct afs_server *server, size_t count,
+			 struct afs_callback_break *callbacks)
+{
+	_enter("%p,%zu,", server, count);
+
+	ASSERT(server != NULL);
+
+	while (count > 0)
+		afs_break_some_callbacks(server, callbacks, &count);
+}