From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration 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 Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- io_uring/eventfd.c | 173 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 173 insertions(+) create mode 100644 io_uring/eventfd.c (limited to 'io_uring/eventfd.c') diff --git a/io_uring/eventfd.c b/io_uring/eventfd.c new file mode 100644 index 000000000..63fe6e5d7 --- /dev/null +++ b/io_uring/eventfd.c @@ -0,0 +1,173 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include +#include +#include +#include + +#include "io-wq.h" +#include "eventfd.h" + +struct io_ev_fd { + struct eventfd_ctx *cq_ev_fd; + unsigned int eventfd_async; + /* protected by ->completion_lock */ + unsigned last_cq_tail; + refcount_t refs; + atomic_t ops; + struct rcu_head rcu; +}; + +enum { + IO_EVENTFD_OP_SIGNAL_BIT, +}; + +static void io_eventfd_free(struct rcu_head *rcu) +{ + struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu); + + eventfd_ctx_put(ev_fd->cq_ev_fd); + kfree(ev_fd); +} + +static void io_eventfd_put(struct io_ev_fd *ev_fd) +{ + if (refcount_dec_and_test(&ev_fd->refs)) + call_rcu(&ev_fd->rcu, io_eventfd_free); +} + +static void io_eventfd_do_signal(struct rcu_head *rcu) +{ + struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu); + + atomic_andnot(BIT(IO_EVENTFD_OP_SIGNAL_BIT), &ev_fd->ops); + eventfd_signal_mask(ev_fd->cq_ev_fd, EPOLL_URING_WAKE); + io_eventfd_put(ev_fd); +} + +/* + * Returns true if the caller should put the ev_fd reference, false if not. + */ +static bool __io_eventfd_signal(struct io_ev_fd *ev_fd, bool defer) +{ + if (!defer && eventfd_signal_allowed()) { + eventfd_signal_mask(ev_fd->cq_ev_fd, EPOLL_URING_WAKE); + return true; + } + if (!atomic_fetch_or(BIT(IO_EVENTFD_OP_SIGNAL_BIT), &ev_fd->ops)) { + call_rcu_hurry(&ev_fd->rcu, io_eventfd_do_signal); + return false; + } + return true; +} + +/* + * Trigger if eventfd_async isn't set, or if it's set and the caller is + * an async worker. + */ +static bool io_eventfd_trigger(struct io_ev_fd *ev_fd) +{ + return !ev_fd->eventfd_async || io_wq_current_is_worker(); +} + +void io_eventfd_signal(struct io_ring_ctx *ctx, bool cqe_event, bool defer) +{ + bool skip = false; + struct io_ev_fd *ev_fd; + struct io_rings *rings; + + guard(rcu)(); + + rings = rcu_dereference(ctx->rings_rcu); + if (!rings) + return; + if (READ_ONCE(rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED) + return; + ev_fd = rcu_dereference(ctx->io_ev_fd); + /* + * Check again if ev_fd exists in case an io_eventfd_unregister call + * completed between the NULL check of ctx->io_ev_fd at the start of + * the function and rcu_read_lock. + */ + if (!ev_fd) + return; + if (!io_eventfd_trigger(ev_fd) || !refcount_inc_not_zero(&ev_fd->refs)) + return; + + if (cqe_event) { + /* + * Eventfd should only get triggered when at least one event + * has been posted. Some applications rely on the eventfd + * notification count only changing IFF a new CQE has been + * added to the CQ ring. There's no dependency on 1:1 + * relationship between how many times this function is called + * (and hence the eventfd count) and number of CQEs posted to + * the CQ ring. + */ + spin_lock(&ctx->completion_lock); + skip = ctx->cached_cq_tail == ev_fd->last_cq_tail; + ev_fd->last_cq_tail = ctx->cached_cq_tail; + spin_unlock(&ctx->completion_lock); + } + + if (skip || __io_eventfd_signal(ev_fd, defer)) + io_eventfd_put(ev_fd); +} + +int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg, + unsigned int eventfd_async) +{ + struct io_ev_fd *ev_fd; + __s32 __user *fds = arg; + int fd; + + ev_fd = rcu_dereference_protected(ctx->io_ev_fd, + lockdep_is_held(&ctx->uring_lock)); + if (ev_fd) + return -EBUSY; + + if (copy_from_user(&fd, fds, sizeof(*fds))) + return -EFAULT; + + ev_fd = kmalloc_obj(*ev_fd); + if (!ev_fd) + return -ENOMEM; + + ev_fd->cq_ev_fd = eventfd_ctx_fdget(fd); + if (IS_ERR(ev_fd->cq_ev_fd)) { + int ret = PTR_ERR(ev_fd->cq_ev_fd); + + kfree(ev_fd); + return ret; + } + + spin_lock(&ctx->completion_lock); + ev_fd->last_cq_tail = ctx->cached_cq_tail; + spin_unlock(&ctx->completion_lock); + + ev_fd->eventfd_async = eventfd_async; + ctx->int_flags |= IO_RING_F_HAS_EVFD; + refcount_set(&ev_fd->refs, 1); + atomic_set(&ev_fd->ops, 0); + rcu_assign_pointer(ctx->io_ev_fd, ev_fd); + return 0; +} + +int io_eventfd_unregister(struct io_ring_ctx *ctx) +{ + struct io_ev_fd *ev_fd; + + ev_fd = rcu_dereference_protected(ctx->io_ev_fd, + lockdep_is_held(&ctx->uring_lock)); + if (ev_fd) { + ctx->int_flags &= ~IO_RING_F_HAS_EVFD; + rcu_assign_pointer(ctx->io_ev_fd, NULL); + io_eventfd_put(ev_fd); + return 0; + } + + return -ENXIO; +} -- cgit v1.3.1