1 /* 2 * Copyright (C) 2013 Luigi Rizzo. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23 * SUCH DAMAGE. 24 */ 25 26 #ifndef NET_PARAVIRT_H 27 #define NET_PARAVIRT_H 28 29 /* 30 * $FreeBSD$ 31 * 32 Support for virtio-like communication between host (H) and guest (G) NICs. 33 34 THIS IS EXPERIMENTAL CODE AND SUBJECT TO CHANGE. 35 36 The guest allocates the shared Communication Status Block (csb) and 37 write its physical address at CSBAL and CSBAH (data is little endian). 38 csb->csb_on enables the mode. If disabled, the device acts a regular one. 39 40 Notifications for tx and rx are exchanged without vm exits 41 if possible. In particular (only mentioning csb mode below), 42 the following actions are performed. In the description below, 43 "double check" means verifying again the condition that caused 44 the previous action, and reverting the action if the condition has 45 changed. The condition typically depends on a variable set by the 46 other party, and the double check is done to avoid races. E.g. 47 48 // start with A=0 49 again: 50 // do something 51 if ( cond(C) ) { // C is written by the other side 52 A = 1; 53 // barrier 54 if ( !cond(C) ) { 55 A = 0; 56 goto again; 57 } 58 } 59 60 TX: start from idle: 61 H starts with host_need_txkick=1 when the I/O thread bh is idle. Upon new 62 transmissions, G always updates guest_tdt. If host_need_txkick == 1, 63 G also writes to the TDT, which acts as a kick to H (so pending 64 writes are always dispatched to H as soon as possible.) 65 66 TX: active state: 67 On the kick (TDT write) H sets host_need_txkick == 0 (if not 68 done already by G), and starts an I/O thread trying to consume 69 packets from TDH to guest_tdt, periodically refreshing host_tdh 70 and TDH. When host_tdh == guest_tdt, H sets host_need_txkick=1, 71 and then does the "double check" for race avoidance. 72 73 TX: G runs out of buffers 74 XXX there are two mechanisms, one boolean (using guest_need_txkick) 75 and one with a threshold (using guest_txkick_at). They are mutually 76 exclusive. 77 BOOLEAN: when G has no space, it sets guest_need_txkick=1 and does 78 the double check. If H finds guest_need_txkick== 1 on a write 79 to TDH, it also generates an interrupt. 80 THRESHOLD: G sets guest_txkick_at to the TDH value for which it 81 wants to receive an interrupt. When H detects that TDH moves 82 across guest_txkick_at, it generates an interrupt. 83 This second mechanism reduces the number of interrupts and 84 TDT writes on the transmit side when the host is too slow. 85 86 RX: start from idle 87 G starts with guest_need_rxkick = 1 when the receive ring is empty. 88 As packets arrive, H updates host_rdh (and RDH) and also generates an 89 interrupt when guest_need_rxkick == 1 (so incoming packets are 90 always reported to G as soon as possible, apart from interrupt 91 moderation delays). It also tracks guest_rdt for new buffers. 92 93 RX: active state 94 As the interrupt arrives, G sets guest_need_rxkick = 0 and starts 95 draining packets from the receive ring, while updating guest_rdt 96 When G runs out of packets it sets guest_need_rxkick=1 and does the 97 double check. 98 99 RX: H runs out of buffers 100 XXX there are two mechanisms, one boolean (using host_need_rxkick) 101 and one with a threshold (using host_xxkick_at). They are mutually 102 exclusive. 103 BOOLEAN: when H has no space, it sets host_need_rxkick=1 and does the 104 double check. If G finds host_need_rxkick==1 on updating guest_rdt, 105 it also writes to RDT causing a kick to H. 106 THRESHOLD: H sets host_rxkick_at to the RDT value for which it wants 107 to receive a kick. When G detects that guest_rdt moves across 108 host_rxkick_at, it writes to RDT thus generates a kick. 109 This second mechanism reduces the number of kicks and 110 RDT writes on the receive side when the guest is too slow and 111 would free only a few buffers at a time. 112 113 */ 114 struct paravirt_csb { 115 /* XXX revise the layout to minimize cache bounces. 116 * Usage is described as follows: 117 * [GH][RW][+-0] guest/host reads/writes frequently/rarely/almost never 118 */ 119 /* these are (mostly) written by the guest */ 120 uint32_t guest_tdt; /* GW+ HR+ pkt to transmit */ 121 uint32_t guest_need_txkick; /* GW- HR+ G ran out of tx bufs, request kick */ 122 uint32_t guest_need_rxkick; /* GW- HR+ G ran out of rx pkts, request kick */ 123 uint32_t guest_csb_on; /* GW- HR+ enable paravirtual mode */ 124 uint32_t guest_rdt; /* GW+ HR+ rx buffers available */ 125 uint32_t guest_txkick_at; /* GW- HR+ tx ring pos. where G expects an intr */ 126 uint32_t guest_use_msix; /* GW0 HR0 guest uses MSI-X interrupts. */ 127 uint32_t pad[9]; 128 129 /* these are (mostly) written by the host */ 130 uint32_t host_tdh; /* GR0 HW- shadow register, mostly unused */ 131 uint32_t host_need_txkick; /* GR+ HW- start the iothread */ 132 uint32_t host_txcycles_lim; /* GW- HR- how much to spin before sleep. 133 * set by the guest */ 134 uint32_t host_txcycles; /* GR0 HW- counter, but no need to be exported */ 135 uint32_t host_rdh; /* GR0 HW- shadow register, mostly unused */ 136 uint32_t host_need_rxkick; /* GR+ HW- flush rx queued packets */ 137 uint32_t host_isr; /* GR* HW* shadow copy of ISR */ 138 uint32_t host_rxkick_at; /* GR+ HW- rx ring pos where H expects a kick */ 139 uint32_t vnet_ring_high; /* Vnet ring physical address high. */ 140 uint32_t vnet_ring_low; /* Vnet ring physical address low. */ 141 }; 142 143 #define NET_PARAVIRT_CSB_SIZE 4096 144 #define NET_PARAVIRT_NONE (~((uint32_t)0)) 145 146 #ifdef QEMU_PCI_H 147 148 /* 149 * API functions only available within QEMU 150 */ 151 152 void paravirt_configure_csb(struct paravirt_csb** csb, uint32_t csbbal, 153 uint32_t csbbah, QEMUBH* tx_bh, AddressSpace *as); 154 155 #endif /* QEMU_PCI_H */ 156 157 #endif /* NET_PARAVIRT_H */ 158