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, 117 insertions, 0 deletions

diff --git a/net/ethtool/debug.c b/net/ethtool/debug.c
new file mode 100644
index 000000000..6043916b4
--- /dev/null
+++ b/net/ethtool/debug.c
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include "bitset.h"
+#include "common.h"
+#include "netlink.h"
+
+struct debug_req_info {
+	struct ethnl_req_info		base;
+};
+
+struct debug_reply_data {
+	struct ethnl_reply_data		base;
+	u32				msg_mask;
+};
+
+#define DEBUG_REPDATA(__reply_base) \
+	container_of(__reply_base, struct debug_reply_data, base)
+
+const struct nla_policy ethnl_debug_get_policy[] = {
+	[ETHTOOL_A_DEBUG_HEADER]	=
+		NLA_POLICY_NESTED(ethnl_header_policy),
+};
+
+static int debug_prepare_data(const struct ethnl_req_info *req_base,
+			      struct ethnl_reply_data *reply_base,
+			      const struct genl_info *info)
+{
+	struct debug_reply_data *data = DEBUG_REPDATA(reply_base);
+	struct net_device *dev = reply_base->dev;
+	int ret;
+
+	if (!dev->ethtool_ops->get_msglevel)
+		return -EOPNOTSUPP;
+
+	ret = ethnl_ops_begin(dev);
+	if (ret < 0)
+		return ret;
+	data->msg_mask = dev->ethtool_ops->get_msglevel(dev);
+	ethnl_ops_complete(dev);
+
+	return 0;
+}
+
+static int debug_reply_size(const struct ethnl_req_info *req_base,
+			    const struct ethnl_reply_data *reply_base)
+{
+	const struct debug_reply_data *data = DEBUG_REPDATA(reply_base);
+	bool compact = req_base->flags & ETHTOOL_FLAG_COMPACT_BITSETS;
+
+	return ethnl_bitset32_size(&data->msg_mask, NULL, NETIF_MSG_CLASS_COUNT,
+				   netif_msg_class_names, compact);
+}
+
+static int debug_fill_reply(struct sk_buff *skb,
+			    const struct ethnl_req_info *req_base,
+			    const struct ethnl_reply_data *reply_base)
+{
+	const struct debug_reply_data *data = DEBUG_REPDATA(reply_base);
+	bool compact = req_base->flags & ETHTOOL_FLAG_COMPACT_BITSETS;
+
+	return ethnl_put_bitset32(skb, ETHTOOL_A_DEBUG_MSGMASK, &data->msg_mask,
+				  NULL, NETIF_MSG_CLASS_COUNT,
+				  netif_msg_class_names, compact);
+}
+
+/* DEBUG_SET */
+
+const struct nla_policy ethnl_debug_set_policy[] = {
+	[ETHTOOL_A_DEBUG_HEADER]	=
+		NLA_POLICY_NESTED(ethnl_header_policy),
+	[ETHTOOL_A_DEBUG_MSGMASK]	= { .type = NLA_NESTED },
+};
+
+static int
+ethnl_set_debug_validate(struct ethnl_req_info *req_info,
+			 struct genl_info *info)
+{
+	const struct ethtool_ops *ops = req_info->dev->ethtool_ops;
+
+	return ops->get_msglevel && ops->set_msglevel ? 1 : -EOPNOTSUPP;
+}
+
+static int
+ethnl_set_debug(struct ethnl_req_info *req_info, struct genl_info *info)
+{
+	struct net_device *dev = req_info->dev;
+	struct nlattr **tb = info->attrs;
+	bool mod = false;
+	u32 msg_mask;
+	int ret;
+
+	msg_mask = dev->ethtool_ops->get_msglevel(dev);
+	ret = ethnl_update_bitset32(&msg_mask, NETIF_MSG_CLASS_COUNT,
+				    tb[ETHTOOL_A_DEBUG_MSGMASK],
+				    netif_msg_class_names, info->extack, &mod);
+	if (ret < 0 || !mod)
+		return ret;
+
+	dev->ethtool_ops->set_msglevel(dev, msg_mask);
+	return 1;
+}
+
+const struct ethnl_request_ops ethnl_debug_request_ops = {
+	.request_cmd		= ETHTOOL_MSG_DEBUG_GET,
+	.reply_cmd		= ETHTOOL_MSG_DEBUG_GET_REPLY,
+	.hdr_attr		= ETHTOOL_A_DEBUG_HEADER,
+	.req_info_size		= sizeof(struct debug_req_info),
+	.reply_data_size	= sizeof(struct debug_reply_data),
+
+	.prepare_data		= debug_prepare_data,
+	.reply_size		= debug_reply_size,
+	.fill_reply		= debug_fill_reply,
+
+	.set_validate		= ethnl_set_debug_validate,
+	.set			= ethnl_set_debug,
+	.set_ntf_cmd		= ETHTOOL_MSG_DEBUG_NTF,
+};