V3migration for review

MAINTAINERS

@@ -3173,6 +3173,14 @@ S: Maintained
 F: hw/semihosting/
 F: include/hw/semihosting/
 
+EBPF:
+M: Jason Wang <jasowang@redhat.com>
+R: Andrew Melnychenko <andrew@daynix.com>
+R: Yuri Benditovich <yuri.benditovich@daynix.com>
+S: Maintained
+F: ebpf/*
+F: tools/ebpf/*
+
 Build and test automation
 -------------------------
 Build and test automation

configure

@@ -342,6 +342,7 @@ vhost_vsock="$default_feature"
 vhost_user="no"
 vhost_user_blk_server="auto"
 vhost_user_fs="$default_feature"
+bpf=""
 kvm="auto"
 hax="auto"
 hvf="auto"
@@ -1236,6 +1237,10 @@ for opt do
   ;;
   --enable-membarrier) membarrier="yes"
   ;;
+  --disable-bpf) bpf="no"
+  ;;
+  --enable-bpf) bpf="yes"
+  ;;
   --disable-blobs) blobs="false"
   ;;
   --with-pkgversion=*) pkgversion="$optarg"
@@ -1845,6 +1850,7 @@ disabled with --disable-FEATURE, default is enabled if available
   vhost-user      vhost-user backend support
   vhost-user-blk-server    vhost-user-blk server support
   vhost-vdpa      vhost-vdpa kernel backend support
+  bpf             BPF kernel support
   spice           spice
   rbd             rados block device (rbd)
   libiscsi        iscsi support
@@ -5057,6 +5063,30 @@ else
     membarrier=no
 fi
 
+##########################################
+# check for usable bpf system call
+if test "$bpf" = ""; then
+    have_bpf=no
+    if test "$linux" = "yes" -a "$bigendian" != "yes"; then
+        cat > $TMPC << EOF
+    #include <stdlib.h>
+    #include <bpf/libbpf.h>
+    int main(void) {
+        struct bpf_object *obj = NULL;
+        bpf_object__load(obj);
+        exit(0);
+    }
+EOF
+        if compile_prog "" "-lbpf" ; then
+            have_bpf=yes
+            bpf=yes
+        fi
+    fi
+    if test "$have_bpf" = "no"; then
+      feature_not_found "bpf" "the libbpf is not available"
+    fi
+fi
+
 ##########################################
 # check if rtnetlink.h exists and is useful
 have_rtnetlink=no
@@ -5905,6 +5935,9 @@ fi
 if test "$membarrier" = "yes" ; then
   echo "CONFIG_MEMBARRIER=y" >> $config_host_mak
 fi
+if test "$bpf" = "yes" -a "$bigendian" != "yes" -a "$linux" = "yes" ; then
+  echo "CONFIG_EBPF=y" >> $config_host_mak
+fi
 if test "$signalfd" = "yes" ; then
   echo "CONFIG_SIGNALFD=y" >> $config_host_mak
 fi

docs/ebpf_rss.rst

@@ -0,0 +1,125 @@
+===========================
+eBPF RSS virtio-net support
+===========================
+
+RSS(Receive Side Scaling) is used to distribute network packets to guest virtqueues
+by calculating packet hash. Usually every queue is processed then by a specific guest CPU core.
+
+For now there are 2 RSS implementations in qemu:
+- 'in-qemu' RSS (functions if qemu receives network packets, i.e. vhost=off)
+- eBPF RSS (can function with also with vhost=on)
+
+eBPF support (CONFIG_EBPF) is enabled by 'configure' script.
+To enable eBPF RSS support use './configure --enable-bpf'.
+
+If steering BPF is not set for kernel's TUN module, the TUN uses automatic selection
+of rx virtqueue based on lookup table built according to calculated symmetric hash
+of transmitted packets.
+If steering BPF is set for TUN the BPF code calculates the hash of packet header and
+returns the virtqueue number to place the packet to.
+
+Simplified decision formula:
+
+.. code:: C
+
+    queue_index = indirection_table[hash(<packet data>)%<indirection_table size>]
+
+
+Not for all packets, the hash can/should be calculated.
+
+Note: currently, eBPF RSS does not support hash reporting.
+
+eBPF RSS turned on by different combinations of vhost-net, vitrio-net and tap configurations:
+
+- eBPF is used:
+
+        tap,vhost=off & virtio-net-pci,rss=on,hash=off
+
+- eBPF is used:
+
+        tap,vhost=on & virtio-net-pci,rss=on,hash=off
+
+- 'in-qemu' RSS is used:
+
+        tap,vhost=off & virtio-net-pci,rss=on,hash=on
+
+- eBPF is used, hash population feature is not reported to the guest:
+
+        tap,vhost=on & virtio-net-pci,rss=on,hash=on
+
+If CONFIG_EBPF is not set then only 'in-qemu' RSS is supported.
+Also 'in-qemu' RSS, as a fallback, is used if the eBPF program failed to load or set to TUN.
+
+RSS eBPF program
+----------------
+
+RSS program located in ebpf/rss.bpf.skeleton.h generated by bpftool.
+So the program is part of the qemu binary.
+Initially, the eBPF program was compiled by clang and source code located at tools/ebpf/rss.bpf.c.
+Prerequisites to recompile the eBPF program (regenerate ebpf/rss.bpf.skeleton.h):
+
+        llvm, clang, kernel source tree, bpftool
+        Adjust 'linuxhdrs' in Makefile.ebpf to reflect the location of the kernel source tree
+
+        $ cd ebpf
+        $ make -f Makefile.ebpf
+
+Current eBPF RSS implementation uses 'bounded loops' with 'backward jump instructions' which present in the last kernels.
+Overall eBPF RSS works on kernels 5.8+.
+
+eBPF RSS implementation
+-----------------------
+
+eBPF RSS loading functionality located in ebpf/ebpf_rss.c and ebpf/ebpf_rss.h.
+
+The `struct EBPFRSSContext` structure that holds 4 file descriptors:
+
+- ctx - pointer of the libbpf context.
+- program_fd - file descriptor of the eBPF RSS program.
+- map_configuration - file descriptor of the 'configuration' map. This map contains one element of 'struct EBPFRSSConfig'. This configuration determines eBPF program behavior.
+- map_toeplitz_key - file descriptor of the 'Toeplitz key' map. One element of the 40byte key prepared for the hashing algorithm.
+- map_indirections_table - 128 elements of queue indexes.
+
+`struct EBPFRSSConfig` fields:
+
+- redirect - "boolean" value, should the hash be calculated, on false  - `default_queue` would be used as the final decision.
+- populate_hash - for now, not used. eBPF RSS doesn't support hash reporting.
+- hash_types - binary mask of different hash types. See `VIRTIO_NET_RSS_HASH_TYPE_*` defines. If for packet hash should not be calculated - `default_queue` would be used.
+- indirections_len - length of the indirections table, maximum 128.
+- default_queue - the queue index that used for packet that shouldn't be hashed. For some packets, the hash can't be calculated(g.e ARP).
+
+Functions:
+
+- `ebpf_rss_init()` - sets ctx to NULL, which indicates that EBPFRSSContext is not loaded.
+- `ebpf_rss_load()` - creates 3 maps and loads eBPF program from tun_rss_steering.h. Returns 'true' on success. After that, program_fd can be used to set steering for TAP.
+- `ebpf_rss_set_all()` - sets values for eBPF maps. `indirections_table` length is in EBPFRSSConfig. `toeplitz_key` is VIRTIO_NET_RSS_MAX_KEY_SIZE aka 40 bytes array.
+- `ebpf_rss_unload()` - close all file descriptors and set ctx to NULL.
+
+Simplified eBPF RSS workflow:
+
+.. code:: C
+
+    struct EBPFRSSConfig config;
+    config.redirect = 1;
+    config.hash_types = VIRTIO_NET_RSS_HASH_TYPE_UDPv4 | VIRTIO_NET_RSS_HASH_TYPE_TCPv4;
+    config.indirections_len = VIRTIO_NET_RSS_MAX_TABLE_LEN;
+    config.default_queue = 0;
+
+    uint16_t table[VIRTIO_NET_RSS_MAX_TABLE_LEN] = {...};
+    uint8_t key[VIRTIO_NET_RSS_MAX_KEY_SIZE] = {...};
+
+    struct EBPFRSSContext ctx;
+    ebpf_rss_init(&ctx);
+    ebpf_rss_load(&ctx);
+    ebpf_rss_set_all(&ctx, &config, table, key);
+    if (net_client->info->set_steering_ebpf != NULL) {
+        net_client->info->set_steering_ebpf(net_client, ctx->program_fd);
+    }
+    ...
+    ebpf_unload(&ctx);
+
+
+NetClientState SetSteeringEBPF()
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+For now, `set_steering_ebpf()` method supported by Linux TAP NetClientState. The method requires an eBPF program file descriptor as an argument.

ebpf/ebpf_rss-stub.c

@@ -0,0 +1,40 @@
+/*
+ * eBPF RSS stub file
+ *
+ * Developed by Daynix Computing LTD (http://www.daynix.com)
+ *
+ * Authors:
+ *  Yuri Benditovich <yuri.benditovich@daynix.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "ebpf/ebpf_rss.h"
+
+void ebpf_rss_init(struct EBPFRSSContext *ctx)
+{
+
+}
+
+bool ebpf_rss_is_loaded(struct EBPFRSSContext *ctx)
+{
+    return false;
+}
+
+bool ebpf_rss_load(struct EBPFRSSContext *ctx)
+{
+    return false;
+}
+
+bool ebpf_rss_set_all(struct EBPFRSSContext *ctx, struct EBPFRSSConfig *config,
+                      uint16_t *indirections_table, uint8_t *toeplitz_key)
+{
+    return false;
+}
+
+void ebpf_rss_unload(struct EBPFRSSContext *ctx)
+{
+
+}