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, 308 insertions, 0 deletions

diff --git a/fs/afs/write.c b/fs/afs/write.c
new file mode 100644
index 000000000..7f34b9397
--- /dev/null
+++ b/fs/afs/write.c
@@ -0,0 +1,308 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* handling of writes to regular files and writing back to the server
+ *
+ * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/backing-dev.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/writeback.h>
+#include <linux/netfs.h>
+#include <trace/events/netfs.h>
+#include "internal.h"
+
+/*
+ * completion of write to server
+ */
+static void afs_pages_written_back(struct afs_vnode *vnode, loff_t start, unsigned int len)
+{
+	_enter("{%llx:%llu},{%x @%llx}",
+	       vnode->fid.vid, vnode->fid.vnode, len, start);
+
+	afs_prune_wb_keys(vnode);
+	_leave("");
+}
+
+/*
+ * Find a key to use for the writeback.  We cached the keys used to author the
+ * writes on the vnode.  wreq->netfs_priv2 will contain the last writeback key
+ * record used or NULL and we need to start from there if it's set.
+ * wreq->netfs_priv will be set to the key itself or NULL.
+ */
+static void afs_get_writeback_key(struct netfs_io_request *wreq)
+{
+	struct afs_wb_key *wbk, *old = wreq->netfs_priv2;
+	struct afs_vnode *vnode = AFS_FS_I(wreq->inode);
+
+	key_put(wreq->netfs_priv);
+	wreq->netfs_priv = NULL;
+	wreq->netfs_priv2 = NULL;
+
+	spin_lock(&vnode->wb_lock);
+	if (old)
+		wbk = list_next_entry(old, vnode_link);
+	else
+		wbk = list_first_entry(&vnode->wb_keys, struct afs_wb_key, vnode_link);
+
+	list_for_each_entry_from(wbk, &vnode->wb_keys, vnode_link) {
+		_debug("wbk %u", key_serial(wbk->key));
+		if (key_validate(wbk->key) == 0) {
+			refcount_inc(&wbk->usage);
+			wreq->netfs_priv = key_get(wbk->key);
+			wreq->netfs_priv2 = wbk;
+			_debug("USE WB KEY %u", key_serial(wbk->key));
+			break;
+		}
+	}
+
+	spin_unlock(&vnode->wb_lock);
+
+	afs_put_wb_key(old);
+}
+
+static void afs_store_data_success(struct afs_operation *op)
+{
+	struct afs_vnode *vnode = op->file[0].vnode;
+
+	op->ctime = op->file[0].scb.status.mtime_client;
+	afs_vnode_commit_status(op, &op->file[0]);
+	if (!afs_op_error(op)) {
+		afs_pages_written_back(vnode, op->store.pos, op->store.size);
+		afs_stat_v(vnode, n_stores);
+		atomic_long_add(op->store.size, &afs_v2net(vnode)->n_store_bytes);
+	}
+}
+
+static const struct afs_operation_ops afs_store_data_operation = {
+	.issue_afs_rpc	= afs_fs_store_data,
+	.issue_yfs_rpc	= yfs_fs_store_data,
+	.success	= afs_store_data_success,
+};
+
+/*
+ * Prepare a subrequest to write to the server.  This sets the max_len
+ * parameter.
+ */
+void afs_prepare_write(struct netfs_io_subrequest *subreq)
+{
+	struct netfs_io_stream *stream = &subreq->rreq->io_streams[subreq->stream_nr];
+
+	//if (test_bit(NETFS_SREQ_RETRYING, &subreq->flags))
+	//	subreq->max_len = 512 * 1024;
+	//else
+	stream->sreq_max_len = 256 * 1024 * 1024;
+}
+
+/*
+ * Issue a subrequest to write to the server.
+ */
+static void afs_issue_write_worker(struct work_struct *work)
+{
+	struct netfs_io_subrequest *subreq = container_of(work, struct netfs_io_subrequest, work);
+	struct netfs_io_request *wreq = subreq->rreq;
+	struct afs_operation *op;
+	struct afs_vnode *vnode = AFS_FS_I(wreq->inode);
+	unsigned long long pos = subreq->start + subreq->transferred;
+	size_t len = subreq->len - subreq->transferred;
+	int ret = -ENOKEY;
+
+	_enter("R=%x[%x],%s{%llx:%llu.%u},%llx,%zx",
+	       wreq->debug_id, subreq->debug_index,
+	       vnode->volume->name,
+	       vnode->fid.vid,
+	       vnode->fid.vnode,
+	       vnode->fid.unique,
+	       pos, len);
+
+#if 0 // Error injection
+	if (subreq->debug_index == 3)
+		return netfs_write_subrequest_terminated(subreq, -ENOANO);
+
+	if (!subreq->retry_count) {
+		set_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
+		return netfs_write_subrequest_terminated(subreq, -EAGAIN);
+	}
+#endif
+
+	op = afs_alloc_operation(wreq->netfs_priv, vnode->volume);
+	if (IS_ERR(op))
+		return netfs_write_subrequest_terminated(subreq, -EAGAIN);
+
+	afs_op_set_vnode(op, 0, vnode);
+	op->file[0].dv_delta	= 1;
+	op->file[0].modification = true;
+	op->store.pos		= pos;
+	op->store.size		= len;
+	op->flags		|= AFS_OPERATION_UNINTR;
+	op->ops			= &afs_store_data_operation;
+
+	afs_begin_vnode_operation(op);
+
+	op->store.write_iter	= &subreq->io_iter;
+	op->store.i_size	= umax(pos + len, netfs_read_remote_i_size(&vnode->netfs.inode));
+	op->mtime		= inode_get_mtime(&vnode->netfs.inode);
+
+	afs_wait_for_operation(op);
+	ret = afs_put_operation(op);
+	switch (ret) {
+	case 0:
+		__set_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
+		break;
+	case -EACCES:
+	case -EPERM:
+	case -ENOKEY:
+	case -EKEYEXPIRED:
+	case -EKEYREJECTED:
+	case -EKEYREVOKED:
+		/* If there are more keys we can try, use the retry algorithm
+		 * to rotate the keys.
+		 */
+		if (wreq->netfs_priv2)
+			set_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
+		break;
+	}
+
+	netfs_write_subrequest_terminated(subreq, ret < 0 ? ret : subreq->len);
+}
+
+void afs_issue_write(struct netfs_io_subrequest *subreq)
+{
+	subreq->work.func = afs_issue_write_worker;
+	if (!queue_work(system_dfl_wq, &subreq->work))
+		WARN_ON_ONCE(1);
+}
+
+/*
+ * Writeback calls this when it finds a folio that needs uploading.  This isn't
+ * called if writeback only has copy-to-cache to deal with.
+ */
+void afs_begin_writeback(struct netfs_io_request *wreq)
+{
+	if (S_ISREG(wreq->inode->i_mode))
+		afs_get_writeback_key(wreq);
+}
+
+/*
+ * Prepare to retry the writes in request.  Use this to try rotating the
+ * available writeback keys.
+ */
+void afs_retry_request(struct netfs_io_request *wreq, struct netfs_io_stream *stream)
+{
+	struct netfs_io_subrequest *subreq =
+		list_first_entry(&stream->subrequests,
+				 struct netfs_io_subrequest, rreq_link);
+
+	switch (wreq->origin) {
+	case NETFS_READAHEAD:
+	case NETFS_READPAGE:
+	case NETFS_READ_GAPS:
+	case NETFS_READ_SINGLE:
+	case NETFS_READ_FOR_WRITE:
+	case NETFS_UNBUFFERED_READ:
+	case NETFS_DIO_READ:
+		return;
+	default:
+		break;
+	}
+
+	switch (subreq->error) {
+	case -EACCES:
+	case -EPERM:
+	case -ENOKEY:
+	case -EKEYEXPIRED:
+	case -EKEYREJECTED:
+	case -EKEYREVOKED:
+		afs_get_writeback_key(wreq);
+		if (!wreq->netfs_priv)
+			stream->failed = true;
+		break;
+	}
+}
+
+/*
+ * write some of the pending data back to the server
+ */
+int afs_writepages(struct address_space *mapping, struct writeback_control *wbc)
+{
+	struct afs_vnode *vnode = AFS_FS_I(mapping->host);
+	int ret;
+
+	/* We have to be careful as we can end up racing with setattr()
+	 * truncating the pagecache since the caller doesn't take a lock here
+	 * to prevent it.
+	 */
+	if (wbc->sync_mode == WB_SYNC_ALL)
+		down_read(&vnode->validate_lock);
+	else if (!down_read_trylock(&vnode->validate_lock))
+		return 0;
+
+	ret = netfs_writepages(mapping, wbc);
+	up_read(&vnode->validate_lock);
+	return ret;
+}
+
+/*
+ * flush any dirty pages for this process, and check for write errors.
+ * - the return status from this call provides a reliable indication of
+ *   whether any write errors occurred for this process.
+ */
+int afs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
+{
+	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
+	struct afs_file *af = file->private_data;
+	int ret;
+
+	_enter("{%llx:%llu},{n=%pD},%d",
+	       vnode->fid.vid, vnode->fid.vnode, file,
+	       datasync);
+
+	ret = afs_validate(vnode, af->key);
+	if (ret < 0)
+		return ret;
+
+	return file_write_and_wait_range(file, start, end);
+}
+
+/*
+ * notification that a previously read-only page is about to become writable
+ * - if it returns an error, the caller will deliver a bus error signal
+ */
+vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
+{
+	struct file *file = vmf->vma->vm_file;
+
+	if (afs_validate(AFS_FS_I(file_inode(file)), afs_file_key(file)) < 0)
+		return VM_FAULT_SIGBUS;
+	return netfs_page_mkwrite(vmf, NULL);
+}
+
+/*
+ * Prune the keys cached for writeback.  The caller must hold vnode->wb_lock.
+ */
+void afs_prune_wb_keys(struct afs_vnode *vnode)
+{
+	LIST_HEAD(graveyard);
+	struct afs_wb_key *wbk, *tmp;
+
+	/* Discard unused keys */
+	spin_lock(&vnode->wb_lock);
+
+	if (!mapping_tagged(&vnode->netfs.inode.i_data, PAGECACHE_TAG_WRITEBACK) &&
+	    !mapping_tagged(&vnode->netfs.inode.i_data, PAGECACHE_TAG_DIRTY)) {
+		list_for_each_entry_safe(wbk, tmp, &vnode->wb_keys, vnode_link) {
+			if (refcount_read(&wbk->usage) == 1)
+				list_move(&wbk->vnode_link, &graveyard);
+		}
+	}
+
+	spin_unlock(&vnode->wb_lock);
+
+	while (!list_empty(&graveyard)) {
+		wbk = list_entry(graveyard.next, struct afs_wb_key, vnode_link);
+		list_del(&wbk->vnode_link);
+		afs_put_wb_key(wbk);
+	}
+}