kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 273 insertions, 0 deletions

diff --git a/drivers/virt/acrn/ioeventfd.c b/drivers/virt/acrn/ioeventfd.c
new file mode 100644
index 000000000..66fe9f3ce
--- /dev/null
+++ b/drivers/virt/acrn/ioeventfd.c
@@ -0,0 +1,273 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ACRN HSM eventfd - use eventfd objects to signal expected I/O requests
+ *
+ * Copyright (C) 2020 Intel Corporation. All rights reserved.
+ *
+ * Authors:
+ *	Shuo Liu <shuo.a.liu@intel.com>
+ *	Yakui Zhao <yakui.zhao@intel.com>
+ */
+
+#include <linux/eventfd.h>
+#include <linux/slab.h>
+
+#include "acrn_drv.h"
+
+/**
+ * struct hsm_ioeventfd - Properties of HSM ioeventfd
+ * @list:	Entry within &acrn_vm.ioeventfds of ioeventfds of a VM
+ * @eventfd:	Eventfd of the HSM ioeventfd
+ * @addr:	Address of I/O range
+ * @data:	Data for matching
+ * @length:	Length of I/O range
+ * @type:	Type of I/O range (ACRN_IOREQ_TYPE_MMIO/ACRN_IOREQ_TYPE_PORTIO)
+ * @wildcard:	Data matching or not
+ */
+struct hsm_ioeventfd {
+	struct list_head	list;
+	struct eventfd_ctx	*eventfd;
+	u64			addr;
+	u64			data;
+	int			length;
+	int			type;
+	bool			wildcard;
+};
+
+static inline int ioreq_type_from_flags(int flags)
+{
+	return flags & ACRN_IOEVENTFD_FLAG_PIO ?
+		       ACRN_IOREQ_TYPE_PORTIO : ACRN_IOREQ_TYPE_MMIO;
+}
+
+static void acrn_ioeventfd_shutdown(struct acrn_vm *vm, struct hsm_ioeventfd *p)
+{
+	lockdep_assert_held(&vm->ioeventfds_lock);
+
+	eventfd_ctx_put(p->eventfd);
+	list_del(&p->list);
+	kfree(p);
+}
+
+static bool hsm_ioeventfd_is_conflict(struct acrn_vm *vm,
+				      struct hsm_ioeventfd *ioeventfd)
+{
+	struct hsm_ioeventfd *p;
+
+	lockdep_assert_held(&vm->ioeventfds_lock);
+
+	/* Either one is wildcard, the data matching will be skipped. */
+	list_for_each_entry(p, &vm->ioeventfds, list)
+		if (p->eventfd == ioeventfd->eventfd &&
+		    p->addr == ioeventfd->addr &&
+		    p->type == ioeventfd->type &&
+		    (p->wildcard || ioeventfd->wildcard ||
+			p->data == ioeventfd->data))
+			return true;
+
+	return false;
+}
+
+/*
+ * Assign an eventfd to a VM and create a HSM ioeventfd associated with the
+ * eventfd. The properties of the HSM ioeventfd are built from a &struct
+ * acrn_ioeventfd.
+ */
+static int acrn_ioeventfd_assign(struct acrn_vm *vm,
+				 struct acrn_ioeventfd *args)
+{
+	struct eventfd_ctx *eventfd;
+	struct hsm_ioeventfd *p;
+	int ret;
+
+	/* Check for range overflow */
+	if (args->addr + args->len < args->addr)
+		return -EINVAL;
+
+	/*
+	 * Currently, acrn_ioeventfd is used to support vhost. 1,2,4,8 width
+	 * accesses can cover vhost's requirements.
+	 */
+	if (!(args->len == 1 || args->len == 2 ||
+	      args->len == 4 || args->len == 8))
+		return -EINVAL;
+
+	eventfd = eventfd_ctx_fdget(args->fd);
+	if (IS_ERR(eventfd))
+		return PTR_ERR(eventfd);
+
+	p = kzalloc_obj(*p);
+	if (!p) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	INIT_LIST_HEAD(&p->list);
+	p->addr = args->addr;
+	p->length = args->len;
+	p->eventfd = eventfd;
+	p->type = ioreq_type_from_flags(args->flags);
+
+	/*
+	 * ACRN_IOEVENTFD_FLAG_DATAMATCH flag is set in virtio 1.0 support, the
+	 * writing of notification register of each virtqueue may trigger the
+	 * notification. There is no data matching requirement.
+	 */
+	if (args->flags & ACRN_IOEVENTFD_FLAG_DATAMATCH)
+		p->data = args->data;
+	else
+		p->wildcard = true;
+
+	mutex_lock(&vm->ioeventfds_lock);
+
+	if (hsm_ioeventfd_is_conflict(vm, p)) {
+		ret = -EEXIST;
+		goto unlock_fail;
+	}
+
+	/* register the I/O range into ioreq client */
+	ret = acrn_ioreq_range_add(vm->ioeventfd_client, p->type,
+				   p->addr, p->addr + p->length - 1);
+	if (ret < 0)
+		goto unlock_fail;
+
+	list_add_tail(&p->list, &vm->ioeventfds);
+	mutex_unlock(&vm->ioeventfds_lock);
+
+	return 0;
+
+unlock_fail:
+	mutex_unlock(&vm->ioeventfds_lock);
+	kfree(p);
+fail:
+	eventfd_ctx_put(eventfd);
+	return ret;
+}
+
+static int acrn_ioeventfd_deassign(struct acrn_vm *vm,
+				   struct acrn_ioeventfd *args)
+{
+	struct hsm_ioeventfd *p;
+	struct eventfd_ctx *eventfd;
+
+	eventfd = eventfd_ctx_fdget(args->fd);
+	if (IS_ERR(eventfd))
+		return PTR_ERR(eventfd);
+
+	mutex_lock(&vm->ioeventfds_lock);
+	list_for_each_entry(p, &vm->ioeventfds, list) {
+		if (p->eventfd != eventfd)
+			continue;
+
+		acrn_ioreq_range_del(vm->ioeventfd_client, p->type,
+				     p->addr, p->addr + p->length - 1);
+		acrn_ioeventfd_shutdown(vm, p);
+		break;
+	}
+	mutex_unlock(&vm->ioeventfds_lock);
+
+	eventfd_ctx_put(eventfd);
+	return 0;
+}
+
+static struct hsm_ioeventfd *hsm_ioeventfd_match(struct acrn_vm *vm, u64 addr,
+						 u64 data, int len, int type)
+{
+	struct hsm_ioeventfd *p = NULL;
+
+	lockdep_assert_held(&vm->ioeventfds_lock);
+
+	list_for_each_entry(p, &vm->ioeventfds, list) {
+		if (p->type == type && p->addr == addr && p->length >= len &&
+		    (p->wildcard || p->data == data))
+			return p;
+	}
+
+	return NULL;
+}
+
+static int acrn_ioeventfd_handler(struct acrn_ioreq_client *client,
+				  struct acrn_io_request *req)
+{
+	struct hsm_ioeventfd *p;
+	u64 addr, val;
+	int size;
+
+	if (req->type == ACRN_IOREQ_TYPE_MMIO) {
+		/*
+		 * I/O requests are dispatched by range check only, so a
+		 * acrn_ioreq_client need process both READ and WRITE accesses
+		 * of same range. READ accesses are safe to be ignored here
+		 * because virtio PCI devices write the notify registers for
+		 * notification.
+		 */
+		if (req->reqs.mmio_request.direction == ACRN_IOREQ_DIR_READ) {
+			/* reading does nothing and return 0 */
+			req->reqs.mmio_request.value = 0;
+			return 0;
+		}
+		addr = req->reqs.mmio_request.address;
+		size = req->reqs.mmio_request.size;
+		val = req->reqs.mmio_request.value;
+	} else {
+		if (req->reqs.pio_request.direction == ACRN_IOREQ_DIR_READ) {
+			/* reading does nothing and return 0 */
+			req->reqs.pio_request.value = 0;
+			return 0;
+		}
+		addr = req->reqs.pio_request.address;
+		size = req->reqs.pio_request.size;
+		val = req->reqs.pio_request.value;
+	}
+
+	mutex_lock(&client->vm->ioeventfds_lock);
+	p = hsm_ioeventfd_match(client->vm, addr, val, size, req->type);
+	if (p)
+		eventfd_signal(p->eventfd);
+	mutex_unlock(&client->vm->ioeventfds_lock);
+
+	return 0;
+}
+
+int acrn_ioeventfd_config(struct acrn_vm *vm, struct acrn_ioeventfd *args)
+{
+	int ret;
+
+	if (args->flags & ACRN_IOEVENTFD_FLAG_DEASSIGN)
+		ret = acrn_ioeventfd_deassign(vm, args);
+	else
+		ret = acrn_ioeventfd_assign(vm, args);
+
+	return ret;
+}
+
+int acrn_ioeventfd_init(struct acrn_vm *vm)
+{
+	char name[ACRN_NAME_LEN];
+
+	mutex_init(&vm->ioeventfds_lock);
+	INIT_LIST_HEAD(&vm->ioeventfds);
+	snprintf(name, sizeof(name), "ioeventfd-%u", vm->vmid);
+	vm->ioeventfd_client = acrn_ioreq_client_create(vm,
+							acrn_ioeventfd_handler,
+							NULL, false, name);
+	if (!vm->ioeventfd_client) {
+		dev_err(acrn_dev.this_device, "Failed to create ioeventfd ioreq client!\n");
+		return -EINVAL;
+	}
+
+	dev_dbg(acrn_dev.this_device, "VM %u ioeventfd init.\n", vm->vmid);
+	return 0;
+}
+
+void acrn_ioeventfd_deinit(struct acrn_vm *vm)
+{
+	struct hsm_ioeventfd *p, *next;
+
+	dev_dbg(acrn_dev.this_device, "VM %u ioeventfd deinit.\n", vm->vmid);
+	acrn_ioreq_client_destroy(vm->ioeventfd_client);
+	mutex_lock(&vm->ioeventfds_lock);
+	list_for_each_entry_safe(p, next, &vm->ioeventfds, list)
+		acrn_ioeventfd_shutdown(vm, p);
+	mutex_unlock(&vm->ioeventfds_lock);
+}