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, 194 insertions, 0 deletions

diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
new file mode 100644
index 000000000..c98d43a7a
--- /dev/null
+++ b/drivers/md/raid1.h
@@ -0,0 +1,194 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _RAID1_H
+#define _RAID1_H
+
+/*
+ * each barrier unit size is 64MB fow now
+ * note: it must be larger than RESYNC_DEPTH
+ */
+#define BARRIER_UNIT_SECTOR_BITS	17
+#define BARRIER_UNIT_SECTOR_SIZE	(1<<17)
+/*
+ * In struct r1conf, the following members are related to I/O barrier
+ * buckets,
+ *	atomic_t	*nr_pending;
+ *	atomic_t	*nr_waiting;
+ *	atomic_t	*nr_queued;
+ *	atomic_t	*barrier;
+ * Each of them points to array of atomic_t variables, each array is
+ * designed to have BARRIER_BUCKETS_NR elements and occupy a single
+ * memory page. The data width of atomic_t variables is 4 bytes, equal
+ * to 1<<(ilog2(sizeof(atomic_t))), BARRIER_BUCKETS_NR_BITS is defined
+ * as (PAGE_SHIFT - ilog2(sizeof(int))) to make sure an array of
+ * atomic_t variables with BARRIER_BUCKETS_NR elements just exactly
+ * occupies a single memory page.
+ */
+#define BARRIER_BUCKETS_NR_BITS		(PAGE_SHIFT - ilog2(sizeof(atomic_t)))
+#define BARRIER_BUCKETS_NR		(1<<BARRIER_BUCKETS_NR_BITS)
+
+/* Note: raid1_info.rdev can be set to NULL asynchronously by raid1_remove_disk.
+ * There are three safe ways to access raid1_info.rdev.
+ * 1/ when holding mddev->reconfig_mutex
+ * 2/ when resync/recovery is known to be happening - i.e. in code that is
+ *    called as part of performing resync/recovery.
+ * 3/ while holding rcu_read_lock(), use rcu_dereference to get the pointer
+ *    and if it is non-NULL, increment rdev->nr_pending before dropping the
+ *    RCU lock.
+ * When .rdev is set to NULL, the nr_pending count checked again and if it has
+ * been incremented, the pointer is put back in .rdev.
+ */
+
+struct raid1_info {
+	struct md_rdev	*rdev;
+	sector_t	head_position;
+
+	/* When choose the best device for a read (read_balance())
+	 * we try to keep sequential reads one the same device
+	 */
+	sector_t	next_seq_sect;
+	sector_t	seq_start;
+};
+
+struct r1conf {
+	struct mddev		*mddev;
+	struct raid1_info	*mirrors;	/* twice 'raid_disks' to
+						 * allow for replacements.
+						 */
+	int			raid_disks;
+	int			nonrot_disks;
+
+	spinlock_t		device_lock;
+
+	/* list of 'struct r1bio' that need to be processed by raid1d,
+	 * whether to retry a read, writeout a resync or recovery
+	 * block, or anything else.
+	 */
+	struct list_head	retry_list;
+	/* A separate list of r1bio which just need raid_end_bio_io called.
+	 * This mustn't happen for writes which had any errors if the superblock
+	 * needs to be written.
+	 */
+	struct list_head	bio_end_io_list;
+
+	/* queue pending writes to be submitted on unplug */
+	struct bio_list		pending_bio_list;
+
+	/* for use when syncing mirrors:
+	 * We don't allow both normal IO and resync/recovery IO at
+	 * the same time - resync/recovery can only happen when there
+	 * is no other IO.  So when either is active, the other has to wait.
+	 * See more details description in raid1.c near raise_barrier().
+	 */
+	wait_queue_head_t	wait_barrier;
+	spinlock_t		resync_lock;
+	atomic_t		nr_sync_pending;
+	atomic_t		*nr_pending;
+	atomic_t		*nr_waiting;
+	atomic_t		*nr_queued;
+	atomic_t		*barrier;
+	int			array_frozen;
+
+	/* Set to 1 if a full sync is needed, (fresh device added).
+	 * Cleared when a sync completes.
+	 */
+	int			fullsync;
+
+	mempool_t		*r1bio_pool;
+	mempool_t		r1buf_pool;
+
+	struct bio_set		bio_split;
+
+	/* temporary buffer to synchronous IO when attempting to repair
+	 * a read error.
+	 */
+	struct page		*tmppage;
+
+	/* When taking over an array from a different personality, we store
+	 * the new thread here until we fully activate the array.
+	 */
+	struct md_thread __rcu	*thread;
+
+	/* Keep track of cluster resync window to send to other
+	 * nodes.
+	 */
+	sector_t		cluster_sync_low;
+	sector_t		cluster_sync_high;
+
+};
+
+/*
+ * this is our 'private' RAID1 bio.
+ *
+ * it contains information about what kind of IO operations were started
+ * for this RAID1 operation, and about their status:
+ */
+
+struct r1bio {
+	atomic_t		remaining; /* 'have we finished' count,
+					    * used from IRQ handlers
+					    */
+	atomic_t		behind_remaining; /* number of write-behind ios remaining
+						 * in this BehindIO request
+						 */
+	sector_t		sector;
+	int			sectors;
+	unsigned long		state;
+	struct mddev		*mddev;
+	/*
+	 * original bio going to /dev/mdx
+	 */
+	struct bio		*master_bio;
+	/*
+	 * if the IO is in READ direction, then this is where we read
+	 */
+	int			read_disk;
+
+	struct list_head	retry_list;
+
+	/*
+	 * When R1BIO_BehindIO is set, we store pages for write behind
+	 * in behind_master_bio.
+	 */
+	struct bio		*behind_master_bio;
+
+	/*
+	 * if the IO is in WRITE direction, then multiple bios are used.
+	 * We choose the number when they are allocated.
+	 */
+	struct bio		*bios[];
+	/* DO NOT PUT ANY NEW FIELDS HERE - bios array is contiguously alloced*/
+};
+
+/* bits for r1bio.state */
+enum r1bio_state {
+	R1BIO_Uptodate,
+	R1BIO_IsSync,
+	R1BIO_BehindIO,
+/* Set ReadError on bios that experience a readerror so that
+ * raid1d knows what to do with them.
+ */
+	R1BIO_ReadError,
+/* For write-behind requests, we call bi_end_io when
+ * the last non-write-behind device completes, providing
+ * any write was successful.  Otherwise we call when
+ * any write-behind write succeeds, otherwise we call
+ * with failure when last write completes (and all failed).
+ *
+ * And for bio_split errors, record that bi_end_io was called
+ * with this flag...
+ */
+	R1BIO_Returned,
+/* If a write for this request means we can clear some
+ * known-bad-block records, we set this flag
+ */
+	R1BIO_MadeGood,
+	R1BIO_WriteError,
+	R1BIO_FailFast,
+};
+
+static inline int sector_to_idx(sector_t sector)
+{
+	return hash_long(sector >> BARRIER_UNIT_SECTOR_BITS,
+			 BARRIER_BUCKETS_NR_BITS);
+}
+#endif