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, 88 insertions, 0 deletions

diff --git a/drivers/md/dm-cache-background-tracker.h b/drivers/md/dm-cache-background-tracker.h
new file mode 100644
index 000000000..47156c14a
--- /dev/null
+++ b/drivers/md/dm-cache-background-tracker.h
@@ -0,0 +1,88 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2017 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_BACKGROUND_WORK_H
+#define DM_CACHE_BACKGROUND_WORK_H
+
+#include <linux/vmalloc.h>
+#include "dm-cache-policy.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The cache policy decides what background work should be performed,
+ * such as promotions, demotions and writebacks. The core cache target
+ * is in charge of performing the work, and does so when it sees fit.
+ *
+ * The background_tracker acts as a go between. Keeping track of future
+ * work that the policy has decided upon, and handing (issuing) it to
+ * the core target when requested.
+ *
+ * There is no locking in this, so calls will probably need to be
+ * protected with a spinlock.
+ */
+
+struct bt_work {
+	struct list_head list;
+	struct rb_node node;
+	struct policy_work work;
+};
+
+extern struct kmem_cache *btracker_work_cache;
+
+struct background_work;
+struct background_tracker;
+
+/*
+ * Create a new tracker, it will not be able to queue more than
+ * 'max_work' entries.
+ */
+struct background_tracker *btracker_create(unsigned int max_work);
+
+/*
+ * Destroy the tracker. No issued, but not complete, work should
+ * exist when this is called. It is fine to have queued but unissued
+ * work.
+ */
+void btracker_destroy(struct background_tracker *b);
+
+unsigned int btracker_nr_demotions_queued(struct background_tracker *b);
+
+/*
+ * Queue some work within the tracker. 'work' should point to the work
+ * to queue, this will be copied (ownership doesn't pass).  If pwork
+ * is not NULL then it will be set to point to the tracker's internal
+ * copy of the work.
+ *
+ * returns -EINVAL iff the work is already queued.  -ENOMEM if the work
+ * couldn't be queued for another reason.
+ */
+int btracker_queue(struct background_tracker *b,
+		   struct policy_work *work,
+		   struct policy_work **pwork);
+
+/*
+ * Hands out the next piece of work to be performed.
+ * Returns -ENODATA if there's no work.
+ */
+int btracker_issue(struct background_tracker *b, struct policy_work **work);
+
+/*
+ * Informs the tracker that the work has been completed and it may forget
+ * about it.
+ */
+void btracker_complete(struct background_tracker *b, struct policy_work *op);
+
+/*
+ * Predicate to see if an origin block is already scheduled for promotion.
+ */
+bool btracker_promotion_already_present(struct background_tracker *b,
+					dm_oblock_t oblock);
+
+/*----------------------------------------------------------------*/
+
+#endif