shadow ioeventfd: add demo (#722)

Signed-off-by: Thanos Makatos <thanos.makatos@nutanix.com>
Reviewed-by: John Levon <john.levon@nutanix.com>

5 files changed, 329 insertions, 0 deletions

diff --git a/README.md b/README.md
index d61412c..abdd757 100644
--- a/README.md
+++ b/README.md
@@ -230,6 +230,14 @@ cat /sys/class/gpio/gpiochip480/base > /sys/class/gpio/export
 for ((i=0;i<12;i++)); do cat /sys/class/gpio/OUT0/value; done
 ```
 
+shadow_ioeventfd_server
+-----------------------
+
+shadow_ioeventfd_server.c and shadow_ioeventfd_speed_test.c are used to
+demonstrate the benefits of shadow ioeventfd, see
+[ioregionfd](./docs/ioregionfd.md) for more information.
+
+
 Other usage notes
 =================
 
diff --git a/docs/ioregionfd.md b/docs/ioregionfd.md
index c09b077..a0cb7d7 100644
--- a/docs/ioregionfd.md
+++ b/docs/ioregionfd.md
@@ -23,3 +23,34 @@ The list of patches:
 * kernel: https://gist.github.com/tmakatos/532afd092a8df2175120d3dbfcd719ef
 * QEMU: https://gist.github.com/tmakatos/57755d2a37a6d53c9ff392e7c34470f6
 * SPDK: https://gist.github.com/tmakatos/f6c10fdaff59c9d629f94bd8e44a53bc
+
+shadow ioeventfd sample
+-----------------------
+
+samples/shadow_ioeventfd_server.c implements a vfio-user server that allows a
+part of its BAR0 to be accessed via a shadow ioeventfd.
+shadow_ioeventfd_speed_test.c is run in the guest. It compares peformance of
+shadow ioeventfd vs. vfio-user messages by repeatedly writing to the part of
+the BAR0 that is handled by shadow ioeventfd and to the part not handled by
+shadow ioeventfd.
+
+To run the sample:
+* Patch and build the kernel and QEMU using above patches.
+* Enable support for shadow ioeventfd in libvfio-user (set `shadow-ieoventfd`
+  to `true` in meson_options.txt and then build libvfio-user.
+* Run samples/shadow_ioeventfd_server, e.g.
+  ```
+  build/samples/shadow_ioeventfd_server /var/run/cntrl
+  ```
+* Start the guest with `intel_iommu=off` in the kernel command line.
+* Bind the device to VFIO:
+  ```
+  modprobe vfio-iommu-type1 allow_unsafe_interrupts=1
+  modprobe vfio-pci ids=4e58:0
+  ```
+  Build and run the test app in the guest (it needs to be copied there first),
+  the BDF needs to be substituted accordingly:
+  ```
+  gcc shadow_ioeventfd_speed_test.c
+  ./a.out 3 0000:00:03.0
+  ```
diff --git a/samples/meson.build b/samples/meson.build
index d1d435c..9807a77 100644
--- a/samples/meson.build
+++ b/samples/meson.build
@@ -92,3 +92,21 @@ lspci = executable(
     include_directories: lib_include_dir,
     install: false,
 )
+
+
+shadow_ioeventfd_server_sources = [
+    'shadow_ioeventfd_server.c',
+]
+
+shadow_ioeventfd_server_deps = [
+    libvfio_user_dep,
+]
+
+shadow_ioeventfd_server = executable(
+    'shadow_ioeventfd_server',
+    shadow_ioeventfd_server_sources,
+    c_args: common_cflags,
+    dependencies: shadow_ioeventfd_server_deps,
+    include_directories: lib_include_dir,
+    install: false,
+)
diff --git a/samples/shadow_ioeventfd_server.c b/samples/shadow_ioeventfd_server.c
new file mode 100644
index 0000000..a737831
--- /dev/null
+++ b/samples/shadow_ioeventfd_server.c
@@ -0,0 +1,175 @@
+/*
+ * Copyright (c) 2022, Nutanix Inc. All rights reserved.
+ *     Author: Thanos Makatos <thanos@nutanix.com>
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions are met:
+ *      * Redistributions of source code must retain the above copyright
+ *        notice, this list of conditions and the following disclaimer.
+ *      * Redistributions in binary form must reproduce the above copyright
+ *        notice, this list of conditions and the following disclaimer in the
+ *        documentation and/or other materials provided with the distribution.
+ *      * Neither the name of Nutanix nor the names of its contributors may be
+ *        used to endorse or promote products derived from this software without
+ *        specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ *  ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
+ *  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ *  (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ *  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ *  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ *  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ *  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+ *  DAMAGE.
+ *
+ */
+
+/*
+ * shadow_ioeventfd_server.c: an example of how to use a shadow ioeventfd.
+ * There is no Linux kernel driver, use samples/shadow_ioeventfd_speed_test.c
+ * in the guest instead.
+ */
+
+#include <stdio.h>
+#include <err.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <assert.h>
+#include <sys/poll.h>
+#include <sys/eventfd.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+
+#include "libvfio-user.h"
+#include "common.h"
+
+static void
+_log(vfu_ctx_t *vfu_ctx UNUSED, int level UNUSED, char const *msg)
+{
+    fprintf(stderr, "%s\n", msg);
+}
+
+static ssize_t
+bar0_cb(vfu_ctx_t *vfu_ctx UNUSED, char * const buf UNUSED,
+        size_t count UNUSED, loff_t offset UNUSED,
+        const bool is_write UNUSED)
+{
+    return count;
+}
+
+int
+main(int argc, char *argv[])
+{
+    int ret;
+    vfu_ctx_t *vfu_ctx;
+    struct pollfd fds[2]; /* one for vfu_ctx, one for shadow_ioeventfd */
+    int fd, bar0_fd;
+
+    if (argc != 2) {
+        errx(EXIT_FAILURE, "missing vfio-user socket path");
+    }
+
+    vfu_ctx = vfu_create_ctx(VFU_TRANS_SOCK, argv[1],
+                             LIBVFIO_USER_FLAG_ATTACH_NB, NULL,
+                             VFU_DEV_TYPE_PCI);
+
+    if (vfu_ctx == NULL) {
+        err(EXIT_FAILURE, "failed to initialize device emulation");
+    }
+
+    ret = vfu_setup_log(vfu_ctx, _log, LOG_ERR);
+    if (ret < 0) {
+        err(EXIT_FAILURE, "failed to setup log");
+    }
+
+    ret = vfu_pci_init(vfu_ctx, VFU_PCI_TYPE_CONVENTIONAL,
+                       PCI_HEADER_TYPE_NORMAL, 0);
+    if (ret < 0) {
+        err(EXIT_FAILURE, "vfu_pci_init() failed");
+    }
+
+    vfu_pci_set_id(vfu_ctx, 0x4e58, 0, 0x0, 0x0);
+
+    ret = vfu_setup_region(vfu_ctx, VFU_PCI_DEV_BAR0_REGION_IDX,
+                           sysconf(_SC_PAGE_SIZE), &bar0_cb,
+                           VFU_REGION_FLAG_RW | VFU_REGION_FLAG_MEM, NULL, 0,
+                           -1, 0);
+    if (ret < 0) {
+        err(EXIT_FAILURE, "failed to setup region");
+    }
+
+    ret = vfu_realize_ctx(vfu_ctx);
+    if (ret < 0) {
+        err(EXIT_FAILURE, "failed to realize device");
+    }
+
+    fds[0] = (struct pollfd) {
+        .fd = vfu_get_poll_fd(vfu_ctx),
+        .events = POLLIN | POLLOUT
+    };
+    ret = poll(fds, 1, -1);
+    assert(ret == 1);
+    ret = vfu_attach_ctx(vfu_ctx);
+    if (ret < 0) {
+         err(EXIT_FAILURE, "failed to attach device");
+    }
+
+    fd = eventfd(0, 0);
+    if (fd == -1) {
+        err(EXIT_FAILURE, "failed to create eventfd");
+    }
+    bar0_fd = syscall(SYS_memfd_create, "BAR0", 0);
+    if (bar0_fd == -1) {
+        err(EXIT_FAILURE, "failed to create BAR0 file");
+    }
+    ret = ftruncate(bar0_fd, sysconf(_SC_PAGESIZE));
+    if (ret == -1) {
+        err(EXIT_FAILURE, "failed to truncate BAR0 file");
+    }
+    ret = vfu_create_ioeventfd(vfu_ctx, VFU_PCI_DEV_BAR0_REGION_IDX,
+                               fd, 0, 4,
+                               0, false, bar0_fd, 0);
+    if (ret == -1) {
+        err(EXIT_FAILURE, "failed to create shadow ioeventfd");
+    }
+
+    fds[0] = (struct pollfd) {
+        .fd = vfu_get_poll_fd(vfu_ctx),
+        .events = POLLIN
+    };
+    fds[1] = (struct pollfd) {
+        .fd = fd,
+        .events = POLLIN
+    };
+
+    do {
+        ret = poll(fds, 2, -1);
+        if (ret < 0) {
+            err(EXIT_FAILURE, "failed to poll(2)");
+        }
+        assert(ret > 0);
+        if (fds[0].revents & (POLLIN)) {
+            ret = vfu_run_ctx(vfu_ctx);
+            if (ret < 0) {
+                if (errno == EAGAIN) {
+                    continue;
+                }
+                if (errno == ENOTCONN) {
+                    return 0;
+                }
+                err(EXIT_FAILURE, "vfu_run_ctx() failed");
+            }
+        }
+        if (fds[1].revents & POLLIN) {
+            eventfd_t value;
+            eventfd_read(fd, &value);
+            bar0_cb(vfu_ctx, NULL, 4, 0, true);
+        }
+    } while (true);
+    return 0;
+}
+
+/* ex: set tabstop=4 shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/samples/shadow_ioeventfd_speed_test.c b/samples/shadow_ioeventfd_speed_test.c
new file mode 100644
index 0000000..5fe036d
--- /dev/null
+++ b/samples/shadow_ioeventfd_speed_test.c
@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2022, Nutanix Inc. All rights reserved.
+ *     Author: Thanos Makatos <thanos@nutanix.com>
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions are met:
+ *      * Redistributions of source code must retain the above copyright
+ *        notice, this list of conditions and the following disclaimer.
+ *      * Redistributions in binary form must reproduce the above copyright
+ *        notice, this list of conditions and the following disclaimer in the
+ *        documentation and/or other materials provided with the distribution.
+ *      * Neither the name of Nutanix nor the names of its contributors may be
+ *        used to endorse or promote products derived from this software without
+ *        specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ *  ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
+ *  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ *  (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ *  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ *  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ *  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ *  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+ *  DAMAGE.
+ *
+ */
+
+/*
+ * shadow_ioeventfd_speed_test.c: application that is run in the guest to
+ * demonstrate the performance benefit of shadow ioeventfd. To be used with
+ * shadow_ioeventfd_server.c on the host.
+ */
+
+#include <stdio.h>
+#include <linux/types.h>
+#include <linux/ioctl.h>
+#include <linux/vfio.h>
+#include <assert.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <linux/limits.h>
+#include <stdlib.h>
+#include <err.h>
+#include <unistd.h>
+#include <sys/time.h>
+
+int main(int argc, char *argv[])
+{
+	int container = open("/dev/vfio/vfio", O_RDWR);
+	assert(container != -1);
+	char path[PATH_MAX];
+	sprintf(path, "/dev/vfio/%d", atoi(argv[1]));
+	int group = open(path, O_RDWR);
+	assert(group != 0);
+	struct vfio_group_status status = { .argsz = sizeof(status) };
+	int ret = ioctl(group, VFIO_GROUP_GET_STATUS, &status);
+	assert(ret != -1);
+	assert(status.flags & VFIO_GROUP_FLAGS_VIABLE);
+	ret = ioctl(group, VFIO_GROUP_SET_CONTAINER, &container);
+	assert(ret != -1);
+	ret = ioctl(container, VFIO_SET_IOMMU, VFIO_TYPE1_IOMMU);
+	assert(ret == 0);
+	int device = ioctl(group, VFIO_GROUP_GET_DEVICE_FD, argv[2]);
+	assert(device >= 0);
+	struct vfio_region_info region_info = {
+		.argsz = sizeof(region_info),
+		.index = 0
+	};
+	ret = ioctl(device, VFIO_DEVICE_GET_REGION_INFO, &region_info);
+	assert(ret == 0);
+	u_int32_t val = 0xdeadbeef;
+	struct timeval t0, t1;
+	const int count = 100000;
+	gettimeofday(&t0, NULL);
+	for (int i = 0; i < count; i++) {
+		ret = pwrite(device, &val, sizeof val, region_info.offset);
+		assert(ret == sizeof val);
+	}
+	gettimeofday(&t1, NULL);
+	printf("shadow:\t%lu us\n",
+	       (t1.tv_sec - t0.tv_sec) * 1000000 + t1.tv_usec - t0.tv_usec);
+	gettimeofday(&t0, NULL);
+	for (int i = 0; i < count; i++) {
+		ret = pwrite(device, &val, sizeof val, region_info.offset + 8);
+		assert(ret == sizeof val);
+	}
+	gettimeofday(&t1, NULL);
+	printf("legacy:\t%lu us\n",
+	       (t1.tv_sec - t0.tv_sec) * 1000000 + t1.tv_usec - t0.tv_usec);
+	return 0;
+}
+
+/* ex: set tabstop=4 shiftwidth=4 softtabstop=4 expandtab: */