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, 38 insertions, 0 deletions

diff --git a/io_uring/sqpoll.h b/io_uring/sqpoll.h
new file mode 100644
index 000000000..fd2f6f29b
--- /dev/null
+++ b/io_uring/sqpoll.h
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+
+struct io_sq_data {
+	refcount_t		refs;
+	atomic_t		park_pending;
+	struct mutex		lock;
+
+	/* ctx's that are using this sqd */
+	struct list_head	ctx_list;
+
+	struct task_struct __rcu *thread;
+	struct wait_queue_head	wait;
+
+	unsigned		sq_thread_idle;
+	int			sq_cpu;
+	pid_t			task_pid;
+	pid_t			task_tgid;
+
+	u64			work_time;
+	unsigned long		state;
+	struct completion	exited;
+};
+
+int io_sq_offload_create(struct io_ring_ctx *ctx, struct io_uring_params *p);
+void io_sq_thread_finish(struct io_ring_ctx *ctx);
+void io_sq_thread_stop(struct io_sq_data *sqd);
+void io_sq_thread_park(struct io_sq_data *sqd);
+void io_sq_thread_unpark(struct io_sq_data *sqd);
+void io_put_sq_data(struct io_sq_data *sqd);
+void io_sqpoll_wait_sq(struct io_ring_ctx *ctx);
+int io_sqpoll_wq_cpu_affinity(struct io_ring_ctx *ctx, cpumask_var_t mask);
+u64 io_sq_cpu_usec(struct task_struct *tsk);
+
+static inline struct task_struct *sqpoll_task_locked(struct io_sq_data *sqd)
+{
+	return rcu_dereference_protected(sqd->thread,
+					 lockdep_is_held(&sqd->lock));
+}