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, 109 insertions, 0 deletions

diff --git a/net/rds/sysctl.c b/net/rds/sysctl.c
new file mode 100644
index 000000000..025f518a4
--- /dev/null
+++ b/net/rds/sysctl.c
@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2006 Oracle.  All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the
+ * OpenIB.org BSD license below:
+ *
+ *     Redistribution and use in source and binary forms, with or
+ *     without modification, are permitted provided that the following
+ *     conditions are met:
+ *
+ *      - Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer.
+ *
+ *      - Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer in the documentation and/or other materials
+ *        provided with the distribution.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/sysctl.h>
+#include <linux/proc_fs.h>
+
+#include "rds.h"
+
+static struct ctl_table_header *rds_sysctl_reg_table;
+
+static unsigned long rds_sysctl_reconnect_min = 1;
+static unsigned long rds_sysctl_reconnect_max = ~0UL;
+
+unsigned long rds_sysctl_reconnect_min_jiffies;
+unsigned long rds_sysctl_reconnect_max_jiffies = HZ;
+
+unsigned int  rds_sysctl_max_unacked_packets = 8;
+unsigned int  rds_sysctl_max_unacked_bytes = (16 << 20);
+
+unsigned int rds_sysctl_ping_enable = 1;
+
+static struct ctl_table rds_sysctl_rds_table[] = {
+	{
+		.procname       = "reconnect_min_delay_ms",
+		.data		= &rds_sysctl_reconnect_min_jiffies,
+		.maxlen         = sizeof(unsigned long),
+		.mode           = 0644,
+		.proc_handler   = proc_doulongvec_ms_jiffies_minmax,
+		.extra1		= &rds_sysctl_reconnect_min,
+		.extra2		= &rds_sysctl_reconnect_max_jiffies,
+	},
+	{
+		.procname       = "reconnect_max_delay_ms",
+		.data		= &rds_sysctl_reconnect_max_jiffies,
+		.maxlen         = sizeof(unsigned long),
+		.mode           = 0644,
+		.proc_handler   = proc_doulongvec_ms_jiffies_minmax,
+		.extra1		= &rds_sysctl_reconnect_min_jiffies,
+		.extra2		= &rds_sysctl_reconnect_max,
+	},
+	{
+		.procname	= "max_unacked_packets",
+		.data		= &rds_sysctl_max_unacked_packets,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+	{
+		.procname	= "max_unacked_bytes",
+		.data		= &rds_sysctl_max_unacked_bytes,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+	{
+		.procname	= "ping_enable",
+		.data		= &rds_sysctl_ping_enable,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+};
+
+void rds_sysctl_exit(void)
+{
+	unregister_net_sysctl_table(rds_sysctl_reg_table);
+}
+
+int rds_sysctl_init(void)
+{
+	rds_sysctl_reconnect_min = msecs_to_jiffies(1);
+	rds_sysctl_reconnect_min_jiffies = rds_sysctl_reconnect_min;
+
+	rds_sysctl_reg_table =
+		register_net_sysctl(&init_net, "net/rds", rds_sysctl_rds_table);
+	if (!rds_sysctl_reg_table)
+		return -ENOMEM;
+	return 0;
+}