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, 167 insertions, 0 deletions

diff --git a/drivers/md/dm-cache-policy-internal.h b/drivers/md/dm-cache-policy-internal.h
new file mode 100644
index 000000000..476a4f679
--- /dev/null
+++ b/drivers/md/dm-cache-policy-internal.h
@@ -0,0 +1,167 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_POLICY_INTERNAL_H
+#define DM_CACHE_POLICY_INTERNAL_H
+
+#include <linux/vmalloc.h>
+#include "dm-cache-policy.h"
+
+/*----------------------------------------------------------------*/
+
+static inline int policy_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock,
+				int data_dir, bool fast_copy, bool *background_queued)
+{
+	return p->lookup(p, oblock, cblock, data_dir, fast_copy, background_queued);
+}
+
+static inline int policy_lookup_with_work(struct dm_cache_policy *p,
+					  dm_oblock_t oblock, dm_cblock_t *cblock,
+					  int data_dir, bool fast_copy,
+					  struct policy_work **work)
+{
+	if (!p->lookup_with_work) {
+		*work = NULL;
+		return p->lookup(p, oblock, cblock, data_dir, fast_copy, NULL);
+	}
+
+	return p->lookup_with_work(p, oblock, cblock, data_dir, fast_copy, work);
+}
+
+static inline int policy_get_background_work(struct dm_cache_policy *p,
+					     bool idle, struct policy_work **result)
+{
+	return p->get_background_work(p, idle, result);
+}
+
+static inline void policy_complete_background_work(struct dm_cache_policy *p,
+						   struct policy_work *work,
+						   bool success)
+{
+	return p->complete_background_work(p, work, success);
+}
+
+static inline void policy_set_dirty(struct dm_cache_policy *p, dm_cblock_t cblock)
+{
+	p->set_dirty(p, cblock);
+}
+
+static inline void policy_clear_dirty(struct dm_cache_policy *p, dm_cblock_t cblock)
+{
+	p->clear_dirty(p, cblock);
+}
+
+static inline int policy_load_mapping(struct dm_cache_policy *p,
+				      dm_oblock_t oblock, dm_cblock_t cblock,
+				      bool dirty, uint32_t hint, bool hint_valid)
+{
+	return p->load_mapping(p, oblock, cblock, dirty, hint, hint_valid);
+}
+
+static inline int policy_invalidate_mapping(struct dm_cache_policy *p,
+					    dm_cblock_t cblock)
+{
+	return p->invalidate_mapping(p, cblock);
+}
+
+static inline uint32_t policy_get_hint(struct dm_cache_policy *p,
+				       dm_cblock_t cblock)
+{
+	return p->get_hint ? p->get_hint(p, cblock) : 0;
+}
+
+static inline dm_cblock_t policy_residency(struct dm_cache_policy *p)
+{
+	return p->residency(p);
+}
+
+static inline void policy_tick(struct dm_cache_policy *p, bool can_block)
+{
+	if (p->tick)
+		return p->tick(p, can_block);
+}
+
+static inline int policy_emit_config_values(struct dm_cache_policy *p, char *result,
+					    unsigned int maxlen, ssize_t *sz_ptr)
+{
+	ssize_t sz = *sz_ptr;
+
+	if (p->emit_config_values)
+		return p->emit_config_values(p, result, maxlen, sz_ptr);
+
+	DMEMIT("0 ");
+	*sz_ptr = sz;
+	return 0;
+}
+
+static inline int policy_set_config_value(struct dm_cache_policy *p,
+					  const char *key, const char *value)
+{
+	return p->set_config_value ? p->set_config_value(p, key, value) : -EINVAL;
+}
+
+static inline void policy_allow_migrations(struct dm_cache_policy *p, bool allow)
+{
+	return p->allow_migrations(p, allow);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Some utility functions commonly used by policies and the core target.
+ */
+static inline size_t bitset_size_in_bytes(unsigned int nr_entries)
+{
+	return sizeof(unsigned long) * dm_div_up(nr_entries, BITS_PER_LONG);
+}
+
+static inline unsigned long *alloc_bitset(unsigned int nr_entries)
+{
+	size_t s = bitset_size_in_bytes(nr_entries);
+
+	return vzalloc(s);
+}
+
+static inline void clear_bitset(void *bitset, unsigned int nr_entries)
+{
+	size_t s = bitset_size_in_bytes(nr_entries);
+
+	memset(bitset, 0, s);
+}
+
+static inline void free_bitset(unsigned long *bits)
+{
+	vfree(bits);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Creates a new cache policy given a policy name, a cache size, an origin size and the block size.
+ */
+struct dm_cache_policy *dm_cache_policy_create(const char *name, dm_cblock_t cache_size,
+					       sector_t origin_size, sector_t block_size);
+
+/*
+ * Destroys the policy.  This drops references to the policy module as well
+ * as calling it's destroy method.  So always use this rather than calling
+ * the policy->destroy method directly.
+ */
+void dm_cache_policy_destroy(struct dm_cache_policy *p);
+
+/*
+ * In case we've forgotten.
+ */
+const char *dm_cache_policy_get_name(struct dm_cache_policy *p);
+
+const unsigned int *dm_cache_policy_get_version(struct dm_cache_policy *p);
+
+size_t dm_cache_policy_get_hint_size(struct dm_cache_policy *p);
+
+/*----------------------------------------------------------------*/
+
+#endif /* DM_CACHE_POLICY_INTERNAL_H */