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, 33 insertions, 0 deletions

diff --git a/drivers/mtd/ubi/wl.h b/drivers/mtd/ubi/wl.h
new file mode 100644
index 000000000..a69169c35
--- /dev/null
+++ b/drivers/mtd/ubi/wl.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef UBI_WL_H
+#define UBI_WL_H
+#ifdef CONFIG_MTD_UBI_FASTMAP
+static void update_fastmap_work_fn(struct work_struct *wrk);
+static struct ubi_wl_entry *find_anchor_wl_entry(struct rb_root *root);
+static struct ubi_wl_entry *get_peb_for_wl(struct ubi_device *ubi);
+static struct ubi_wl_entry *next_peb_for_wl(struct ubi_device *ubi,
+					    bool need_fill);
+static bool need_wear_leveling(struct ubi_device *ubi);
+static void ubi_fastmap_close(struct ubi_device *ubi);
+static inline void ubi_fastmap_init(struct ubi_device *ubi, int *count)
+{
+	if (ubi->fm_disabled)
+		ubi->fm_pool_rsv_cnt = 0;
+	/* Reserve enough LEBs to store two fastmaps and to fill pools. */
+	*count += (ubi->fm_size / ubi->leb_size) * 2 + ubi->fm_pool_rsv_cnt;
+	INIT_WORK(&ubi->fm_work, update_fastmap_work_fn);
+}
+static struct ubi_wl_entry *may_reserve_for_fm(struct ubi_device *ubi,
+					       struct ubi_wl_entry *e,
+					       struct rb_root *root);
+#else /* !CONFIG_MTD_UBI_FASTMAP */
+static struct ubi_wl_entry *get_peb_for_wl(struct ubi_device *ubi);
+static inline void ubi_fastmap_close(struct ubi_device *ubi) { }
+static inline void ubi_fastmap_init(struct ubi_device *ubi, int *count) { }
+static struct ubi_wl_entry *may_reserve_for_fm(struct ubi_device *ubi,
+					       struct ubi_wl_entry *e,
+					       struct rb_root *root) {
+	return e;
+}
+#endif /* CONFIG_MTD_UBI_FASTMAP */
+#endif /* UBI_WL_H */