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, 75 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_debugfs.c b/drivers/scsi/scsi_debugfs.c
new file mode 100644
index 000000000..eb52e39f3
--- /dev/null
+++ b/drivers/scsi/scsi_debugfs.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bitops.h>
+#include <linux/cleanup.h>
+#include <linux/seq_file.h>
+#include <scsi/scsi_cmnd.h>
+#include <scsi/scsi_dbg.h>
+#include <scsi/scsi_host.h>
+#include "scsi_debugfs.h"
+
+#define SCSI_CMD_FLAG_NAME(name)[const_ilog2(SCMD_##name)] = #name
+static const char *const scsi_cmd_flags[] = {
+	SCSI_CMD_FLAG_NAME(TAGGED),
+	SCSI_CMD_FLAG_NAME(INITIALIZED),
+	SCSI_CMD_FLAG_NAME(LAST),
+};
+#undef SCSI_CMD_FLAG_NAME
+
+static int scsi_flags_show(struct seq_file *m, const unsigned long flags,
+			   const char *const *flag_name, int flag_name_count)
+{
+	bool sep = false;
+	int i;
+
+	for_each_set_bit(i, &flags, BITS_PER_LONG) {
+		if (sep)
+			seq_puts(m, "|");
+		sep = true;
+		if (i < flag_name_count && flag_name[i])
+			seq_puts(m, flag_name[i]);
+		else
+			seq_printf(m, "%d", i);
+	}
+	return 0;
+}
+
+static const char *scsi_cmd_list_info(struct scsi_cmnd *cmd)
+{
+	struct Scsi_Host *shost = cmd->device->host;
+	struct scsi_cmnd *cmd2;
+
+	guard(spinlock_irq)(shost->host_lock);
+
+	list_for_each_entry(cmd2, &shost->eh_abort_list, eh_entry)
+		if (cmd == cmd2)
+			return "on eh_abort_list";
+
+	list_for_each_entry(cmd2, &shost->eh_cmd_q, eh_entry)
+		if (cmd == cmd2)
+			return "on eh_cmd_q";
+
+	return NULL;
+}
+
+void scsi_show_rq(struct seq_file *m, struct request *rq)
+{
+	struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
+	int alloc_ms = jiffies_to_msecs(jiffies - cmd->jiffies_at_alloc);
+	int timeout_ms = jiffies_to_msecs(rq->timeout);
+	char buf[80] = "(?)";
+
+	if (cmd->flags & SCMD_INITIALIZED) {
+		const char *list_info = scsi_cmd_list_info(cmd);
+
+		__scsi_format_command(buf, sizeof(buf), cmd->cmnd, cmd->cmd_len);
+		seq_printf(m, ", .cmd=%s, .retries=%d, .allowed=%d, .result = %#x%s%s",
+			   buf, cmd->retries, cmd->allowed, cmd->result,
+			   list_info ? ", " : "", list_info ? : "");
+		seq_printf(m, ", .timeout=%d.%03d, allocated %d.%03d s ago",
+			   timeout_ms / 1000, timeout_ms % 1000,
+			   alloc_ms / 1000, alloc_ms % 1000);
+	}
+	seq_printf(m, ", .flags=");
+	scsi_flags_show(m, cmd->flags, scsi_cmd_flags,
+			ARRAY_SIZE(scsi_cmd_flags));
+}