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, 72 insertions, 0 deletions

diff --git a/sound/firewire/lib.c b/sound/firewire/lib.c
new file mode 100644
index 000000000..654e1a605
--- /dev/null
+++ b/sound/firewire/lib.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * miscellaneous helper functions
+ *
+ * Copyright (c) Clemens Ladisch <clemens@ladisch.de>
+ */
+
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/firewire.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include "lib.h"
+
+#define ERROR_RETRY_DELAY_MS	20
+
+/**
+ * snd_fw_transaction - send a request and wait for its completion
+ * @unit: the driver's unit on the target device
+ * @tcode: the transaction code
+ * @offset: the address in the target's address space
+ * @buffer: input/output data
+ * @length: length of @buffer
+ * @flags: use %FW_FIXED_GENERATION and add the generation value to attempt the
+ *         request only in that generation; use %FW_QUIET to suppress error
+ *         messages
+ *
+ * Submits an asynchronous request to the target device, and waits for the
+ * response.  The node ID and the current generation are derived from @unit.
+ * On a bus reset or an error, the transaction is retried a few times.
+ * Returns zero on success, or a negative error code.
+ */
+int snd_fw_transaction(struct fw_unit *unit, int tcode,
+		       u64 offset, void *buffer, size_t length,
+		       unsigned int flags)
+{
+	struct fw_device *device = fw_parent_device(unit);
+	int generation, rcode, tries = 0;
+
+	generation = flags & FW_GENERATION_MASK;
+	for (;;) {
+		if (!(flags & FW_FIXED_GENERATION)) {
+			generation = device->generation;
+			smp_rmb(); /* node_id vs. generation */
+		}
+		rcode = fw_run_transaction(device->card, tcode,
+					   device->node_id, generation,
+					   device->max_speed, offset,
+					   buffer, length);
+
+		if (rcode == RCODE_COMPLETE)
+			return 0;
+
+		if (rcode == RCODE_GENERATION && (flags & FW_FIXED_GENERATION))
+			return -EAGAIN;
+
+		if (rcode_is_permanent_error(rcode) || ++tries >= 3) {
+			if (!(flags & FW_QUIET))
+				dev_err(&unit->device,
+					"transaction failed: %s\n",
+					fw_rcode_string(rcode));
+			return -EIO;
+		}
+
+		msleep(ERROR_RETRY_DELAY_MS);
+	}
+}
+EXPORT_SYMBOL(snd_fw_transaction);
+
+MODULE_DESCRIPTION("FireWire audio helper functions");
+MODULE_AUTHOR("Clemens Ladisch <clemens@ladisch.de>");
+MODULE_LICENSE("GPL");