KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 141 insertions, 0 deletions

diff --git a/io_uring/notif.c b/io_uring/notif.c
new file mode 100644
index 000000000..efce8ae12
--- /dev/null
+++ b/io_uring/notif.c
@@ -0,0 +1,141 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/slab.h>
+#include <linux/net.h>
+#include <linux/io_uring.h>
+
+#include "io_uring.h"
+#include "notif.h"
+#include "rsrc.h"
+
+static const struct ubuf_info_ops io_ubuf_ops;
+
+static void io_notif_tw_complete(struct io_tw_req tw_req, io_tw_token_t tw)
+{
+	struct io_kiocb *notif = tw_req.req;
+	struct io_notif_data *nd = io_notif_to_data(notif);
+	struct io_ring_ctx *ctx = notif->ctx;
+
+	lockdep_assert_held(&ctx->uring_lock);
+
+	do {
+		notif = cmd_to_io_kiocb(nd);
+
+		if (WARN_ON_ONCE(ctx != notif->ctx))
+			return;
+		lockdep_assert(refcount_read(&nd->uarg.refcnt) == 0);
+
+		if (unlikely(nd->zc_report) && (nd->zc_copied || !nd->zc_used))
+			notif->cqe.res |= IORING_NOTIF_USAGE_ZC_COPIED;
+
+		if (nd->account_pages && notif->ctx->user) {
+			__io_unaccount_mem(notif->ctx->user, nd->account_pages);
+			nd->account_pages = 0;
+		}
+
+		nd = nd->next;
+		io_req_task_complete((struct io_tw_req){notif}, tw);
+	} while (nd);
+}
+
+void io_tx_ubuf_complete(struct sk_buff *skb, struct ubuf_info *uarg,
+			 bool success)
+{
+	struct io_notif_data *nd = container_of(uarg, struct io_notif_data, uarg);
+	struct io_kiocb *notif = cmd_to_io_kiocb(nd);
+	unsigned tw_flags;
+
+	if (nd->zc_report) {
+		if (success && !nd->zc_used && skb)
+			WRITE_ONCE(nd->zc_used, true);
+		else if (!success && !nd->zc_copied)
+			WRITE_ONCE(nd->zc_copied, true);
+	}
+
+	if (!refcount_dec_and_test(&uarg->refcnt))
+		return;
+
+	if (nd->head != nd) {
+		io_tx_ubuf_complete(skb, &nd->head->uarg, success);
+		return;
+	}
+
+	tw_flags = nd->next ? 0 : IOU_F_TWQ_LAZY_WAKE;
+	notif->io_task_work.func = io_notif_tw_complete;
+	__io_req_task_work_add(notif, tw_flags);
+}
+
+static int io_link_skb(struct sk_buff *skb, struct ubuf_info *uarg)
+{
+	struct io_notif_data *nd, *prev_nd;
+	struct io_kiocb *prev_notif, *notif;
+	struct ubuf_info *prev_uarg = skb_zcopy(skb);
+
+	nd = container_of(uarg, struct io_notif_data, uarg);
+	notif = cmd_to_io_kiocb(nd);
+
+	if (!prev_uarg) {
+		net_zcopy_get(&nd->uarg);
+		skb_zcopy_init(skb, &nd->uarg);
+		return 0;
+	}
+	/* handle it separately as we can't link a notif to itself */
+	if (unlikely(prev_uarg == &nd->uarg))
+		return 0;
+	/* we can't join two links together, just request a fresh skb */
+	if (unlikely(nd->head != nd || nd->next))
+		return -EEXIST;
+	/* don't mix zc providers */
+	if (unlikely(prev_uarg->ops != &io_ubuf_ops))
+		return -EEXIST;
+
+	prev_nd = container_of(prev_uarg, struct io_notif_data, uarg);
+	prev_notif = cmd_to_io_kiocb(prev_nd);
+
+	/* make sure all notifications can be finished in the same task_work */
+	if (unlikely(notif->ctx != prev_notif->ctx ||
+		     notif->tctx != prev_notif->tctx))
+		return -EEXIST;
+
+	nd->head = prev_nd->head;
+	nd->next = prev_nd->next;
+	prev_nd->next = nd;
+	net_zcopy_get(&nd->head->uarg);
+	return 0;
+}
+
+static const struct ubuf_info_ops io_ubuf_ops = {
+	.complete = io_tx_ubuf_complete,
+	.link_skb = io_link_skb,
+};
+
+struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx)
+	__must_hold(&ctx->uring_lock)
+{
+	struct io_kiocb *notif;
+	struct io_notif_data *nd;
+
+	if (unlikely(!io_alloc_req(ctx, &notif)))
+		return NULL;
+	notif->ctx = ctx;
+	notif->opcode = IORING_OP_NOP;
+	notif->flags = 0;
+	notif->file = NULL;
+	notif->tctx = current->io_uring;
+	io_get_task_refs(1);
+	notif->file_node = NULL;
+	notif->buf_node = NULL;
+
+	nd = io_notif_to_data(notif);
+	nd->zc_report = false;
+	nd->account_pages = 0;
+	nd->next = NULL;
+	nd->head = nd;
+
+	nd->uarg.flags = IO_NOTIF_UBUF_FLAGS;
+	nd->uarg.ops = &io_ubuf_ops;
+	refcount_set(&nd->uarg.refcnt, 1);
+	return notif;
+}