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, 57 insertions, 0 deletions

diff --git a/io_uring/notif.h b/io_uring/notif.h
new file mode 100644
index 000000000..f3589cfef
--- /dev/null
+++ b/io_uring/notif.h
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/net.h>
+#include <linux/uio.h>
+#include <net/sock.h>
+#include <linux/nospec.h>
+
+#include "rsrc.h"
+
+#define IO_NOTIF_UBUF_FLAGS	(SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN)
+#define IO_NOTIF_SPLICE_BATCH	32
+
+struct io_notif_data {
+	struct file		*file;
+	struct ubuf_info	uarg;
+
+	struct io_notif_data	*next;
+	struct io_notif_data	*head;
+
+	unsigned		account_pages;
+	bool			zc_report;
+	bool			zc_used;
+	bool			zc_copied;
+};
+
+struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx);
+void io_tx_ubuf_complete(struct sk_buff *skb, struct ubuf_info *uarg,
+			 bool success);
+
+static inline struct io_notif_data *io_notif_to_data(struct io_kiocb *notif)
+{
+	return io_kiocb_to_cmd(notif, struct io_notif_data);
+}
+
+static inline void io_notif_flush(struct io_kiocb *notif)
+	__must_hold(&notif->ctx->uring_lock)
+{
+	struct io_notif_data *nd = io_notif_to_data(notif);
+
+	io_tx_ubuf_complete(NULL, &nd->uarg, true);
+}
+
+static inline int io_notif_account_mem(struct io_kiocb *notif, unsigned len)
+{
+	struct io_ring_ctx *ctx = notif->ctx;
+	struct io_notif_data *nd = io_notif_to_data(notif);
+	unsigned nr_pages = (len >> PAGE_SHIFT) + 2;
+	int ret;
+
+	if (ctx->user) {
+		ret = __io_account_mem(ctx->user, nr_pages);
+		if (ret)
+			return ret;
+		nd->account_pages += nr_pages;
+	}
+	return 0;
+}