hw: replace most use of qemu_chr_fe_write with qemu_chr_fe_write_all

The qemu_chr_fe_write method will return -1 on EAGAIN if the
chardev backend write would block. Almost no callers of the
qemu_chr_fe_write() method check the return value, instead
blindly assuming data was successfully sent. In most cases
this will lead to silent data loss on interactive consoles,
but in some cases (eg RNG EGD) it'll just cause corruption
of the protocol being spoken.

We unfortunately can't fix the virtio-console code, due to
a bug in the Linux guest drivers, which would cause the
entire Linux kernel to hang if we delay processing of the
incoming data in any way. Fixing this requires first fixing
the guest driver to not hold spinlocks while writing to the
hvc device backend.

Fixes bug: https://bugs.launchpad.net/qemu/+bug/1586756

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1473170165-540-4-git-send-email-berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

21 files changed, 76 insertions, 16 deletions

diff --git a/hw/char/bcm2835_aux.c b/hw/char/bcm2835_aux.c
index 319f1652f6..f7a845d3e2 100644
--- a/hw/char/bcm2835_aux.c
+++ b/hw/char/bcm2835_aux.c
@@ -169,7 +169,9 @@ static void bcm2835_aux_write(void *opaque, hwaddr offset, uint64_t value,
         /* "DLAB bit set means access baudrate register" is NYI */
         ch = value;
         if (s->chr) {
-            qemu_chr_fe_write(s->chr, &ch, 1);
+            /* XXX this blocks entire thread. Rewrite to use
+             * qemu_chr_fe_write and background I/O callbacks */
+            qemu_chr_fe_write_all(s->chr, &ch, 1);
         }
         break;
 
diff --git a/hw/char/debugcon.c b/hw/char/debugcon.c
index e7f025ec67..4402033861 100644
--- a/hw/char/debugcon.c
+++ b/hw/char/debugcon.c
@@ -60,7 +60,9 @@ static void debugcon_ioport_write(void *opaque, hwaddr addr, uint64_t val,
     printf(" [debugcon: write addr=0x%04" HWADDR_PRIx " val=0x%02" PRIx64 "]\n", addr, val);
 #endif
 
-    qemu_chr_fe_write(s->chr, &ch, 1);
+    /* XXX this blocks entire thread. Rewrite to use
+     * qemu_chr_fe_write and background I/O callbacks */
+    qemu_chr_fe_write_all(s->chr, &ch, 1);
 }
 
 
diff --git a/hw/char/digic-uart.c b/hw/char/digic-uart.c
index c7604e6766..e96a9b2d8d 100644
--- a/hw/char/digic-uart.c
+++ b/hw/char/digic-uart.c
@@ -77,6 +77,8 @@ static void digic_uart_write(void *opaque, hwaddr addr, uint64_t value,
     switch (addr) {
     case R_TX:
         if (s->chr) {
+            /* XXX this blocks entire thread. Rewrite to use
+             * qemu_chr_fe_write and background I/O callbacks */
             qemu_chr_fe_write_all(s->chr, &ch, 1);
         }
         break;
diff --git a/hw/char/escc.c b/hw/char/escc.c
index 31a5f902f9..aa1739762b 100644
--- a/hw/char/escc.c
+++ b/hw/char/escc.c
@@ -557,7 +557,9 @@ static void escc_mem_write(void *opaque, hwaddr addr,
         s->tx = val;
         if (s->wregs[W_TXCTRL2] & TXCTRL2_TXEN) { // tx enabled
             if (s->chr)
-                qemu_chr_fe_write(s->chr, &s->tx, 1);
+                /* XXX this blocks entire thread. Rewrite to use
+                 * qemu_chr_fe_write and background I/O callbacks */
+                qemu_chr_fe_write_all(s->chr, &s->tx, 1);
             else if (s->type == kbd && !s->disabled) {
                 handle_kbd_command(s, val);
             }
diff --git a/hw/char/etraxfs_ser.c b/hw/char/etraxfs_ser.c
index 04ca04fe2c..c99cc5d130 100644
--- a/hw/char/etraxfs_ser.c
+++ b/hw/char/etraxfs_ser.c
@@ -126,7 +126,9 @@ ser_write(void *opaque, hwaddr addr,
     switch (addr)
     {
         case RW_DOUT:
-            qemu_chr_fe_write(s->chr, &ch, 1);
+            /* XXX this blocks entire thread. Rewrite to use
+             * qemu_chr_fe_write and background I/O callbacks */
+            qemu_chr_fe_write_all(s->chr, &ch, 1);
             s->regs[R_INTR] |= 3;
             s->pending_tx = 1;
             s->regs[addr] = value;
diff --git a/hw/char/exynos4210_uart.c b/hw/char/exynos4210_uart.c
index 885ecc027b..1107578138 100644
--- a/hw/char/exynos4210_uart.c
+++ b/hw/char/exynos4210_uart.c
@@ -387,7 +387,9 @@ static void exynos4210_uart_write(void *opaque, hwaddr offset,
             s->reg[I_(UTRSTAT)] &= ~(UTRSTAT_TRANSMITTER_EMPTY |
                     UTRSTAT_Tx_BUFFER_EMPTY);
             ch = (uint8_t)val;
-            qemu_chr_fe_write(s->chr, &ch, 1);
+            /* XXX this blocks entire thread. Rewrite to use
+             * qemu_chr_fe_write and background I/O callbacks */
+            qemu_chr_fe_write_all(s->chr, &ch, 1);
 #if DEBUG_Tx_DATA
             fprintf(stderr, "%c", ch);
 #endif
diff --git a/hw/char/grlib_apbuart.c b/hw/char/grlib_apbuart.c
index 871524c82f..778148a15e 100644
--- a/hw/char/grlib_apbuart.c
+++ b/hw/char/grlib_apbuart.c
@@ -203,7 +203,9 @@ static void grlib_apbuart_write(void *opaque, hwaddr addr,
         /* Transmit when character device available and transmitter enabled */
         if ((uart->chr) && (uart->control & UART_TRANSMIT_ENABLE)) {
             c = value & 0xFF;
-            qemu_chr_fe_write(uart->chr, &c, 1);
+            /* XXX this blocks entire thread. Rewrite to use
+             * qemu_chr_fe_write and background I/O callbacks */
+            qemu_chr_fe_write_all(uart->chr, &c, 1);
             /* Generate interrupt */
             if (uart->control & UART_TRANSMIT_INTERRUPT) {
                 qemu_irq_pulse(uart->irq);
diff --git a/hw/char/imx_serial.c b/hw/char/imx_serial.c
index 44856d671e..5c3fa61e4c 100644
--- a/hw/char/imx_serial.c
+++ b/hw/char/imx_serial.c
@@ -182,7 +182,9 @@ static void imx_serial_write(void *opaque, hwaddr offset,
         ch = value;
         if (s->ucr2 & UCR2_TXEN) {
             if (s->chr) {
-                qemu_chr_fe_write(s->chr, &ch, 1);
+                /* XXX this blocks entire thread. Rewrite to use
+                 * qemu_chr_fe_write and background I/O callbacks */
+                qemu_chr_fe_write_all(s->chr, &ch, 1);
             }
             s->usr1 &= ~USR1_TRDY;
             imx_update(s);
diff --git a/hw/char/ipoctal232.c b/hw/char/ipoctal232.c
index 9ead32af60..2859fdd7fb 100644
--- a/hw/char/ipoctal232.c
+++ b/hw/char/ipoctal232.c
@@ -360,7 +360,9 @@ static void io_write(IPackDevice *ip, uint8_t addr, uint16_t val)
             DPRINTF("Write THR%c (0x%x)\n", channel + 'a', reg);
             if (ch->dev) {
                 uint8_t thr = reg;
-                qemu_chr_fe_write(ch->dev, &thr, 1);
+                /* XXX this blocks entire thread. Rewrite to use
+                 * qemu_chr_fe_write and background I/O callbacks */
+                qemu_chr_fe_write_all(ch->dev, &thr, 1);
             }
         } else {
             DPRINTF("Write THR%c (0x%x), Tx disabled\n", channel + 'a', reg);
diff --git a/hw/char/lm32_juart.c b/hw/char/lm32_juart.c
index 28c2cf702d..cb1ac76731 100644
--- a/hw/char/lm32_juart.c
+++ b/hw/char/lm32_juart.c
@@ -76,6 +76,8 @@ void lm32_juart_set_jtx(DeviceState *d, uint32_t jtx)
 
     s->jtx = jtx;
     if (s->chr) {
+        /* XXX this blocks entire thread. Rewrite to use
+         * qemu_chr_fe_write and background I/O callbacks */
         qemu_chr_fe_write_all(s->chr, &ch, 1);
     }
 }
diff --git a/hw/char/lm32_uart.c b/hw/char/lm32_uart.c
index b5c760dda3..be93697a39 100644
--- a/hw/char/lm32_uart.c
+++ b/hw/char/lm32_uart.c
@@ -178,6 +178,8 @@ static void uart_write(void *opaque, hwaddr addr,
     switch (addr) {
     case R_RXTX:
         if (s->chr) {
+            /* XXX this blocks entire thread. Rewrite to use
+             * qemu_chr_fe_write and background I/O callbacks */
             qemu_chr_fe_write_all(s->chr, &ch, 1);
         }
         break;
diff --git a/hw/char/mcf_uart.c b/hw/char/mcf_uart.c
index 3c0438fd79..c184859c83 100644
--- a/hw/char/mcf_uart.c
+++ b/hw/char/mcf_uart.c
@@ -114,7 +114,9 @@ static void mcf_uart_do_tx(mcf_uart_state *s)
 {
     if (s->tx_enabled && (s->sr & MCF_UART_TxEMP) == 0) {
         if (s->chr)
-            qemu_chr_fe_write(s->chr, (unsigned char *)&s->tb, 1);
+            /* XXX this blocks entire thread. Rewrite to use
+             * qemu_chr_fe_write and background I/O callbacks */
+            qemu_chr_fe_write_all(s->chr, (unsigned char *)&s->tb, 1);
         s->sr |= MCF_UART_TxEMP;
     }
     if (s->tx_enabled) {
diff --git a/hw/char/parallel.c b/hw/char/parallel.c
index fa085667ff..da22e36356 100644
--- a/hw/char/parallel.c
+++ b/hw/char/parallel.c
@@ -129,7 +129,9 @@ parallel_ioport_write_sw(void *opaque, uint32_t addr, uint32_t val)
             if (val & PARA_CTR_STROBE) {
                 s->status &= ~PARA_STS_BUSY;
                 if ((s->control & PARA_CTR_STROBE) == 0)
-                    qemu_chr_fe_write(s->chr, &s->dataw, 1);
+                    /* XXX this blocks entire thread. Rewrite to use
+                     * qemu_chr_fe_write and background I/O callbacks */
+                    qemu_chr_fe_write_all(s->chr, &s->dataw, 1);
             } else {
                 if (s->control & PARA_CTR_INTEN) {
                     s->irq_pending = 1;
diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index c0fbf8a874..786e605fdd 100644
--- a/hw/char/pl011.c
+++ b/hw/char/pl011.c
@@ -146,7 +146,9 @@ static void pl011_write(void *opaque, hwaddr offset,
         /* ??? Check if transmitter is enabled.  */
         ch = value;
         if (s->chr)
-            qemu_chr_fe_write(s->chr, &ch, 1);
+            /* XXX this blocks entire thread. Rewrite to use
+             * qemu_chr_fe_write and background I/O callbacks */
+            qemu_chr_fe_write_all(s->chr, &ch, 1);
         s->int_level |= PL011_INT_TX;
         pl011_update(s);
         break;
diff --git a/hw/char/sclpconsole-lm.c b/hw/char/sclpconsole-lm.c
index dbe753147b..9a563269e6 100644
--- a/hw/char/sclpconsole-lm.c
+++ b/hw/char/sclpconsole-lm.c
@@ -89,7 +89,9 @@ static void chr_read(void *opaque, const uint8_t *buf, int size)
     scon->buf[scon->length] = *buf;
     scon->length += 1;
     if (scon->echo) {
-        qemu_chr_fe_write(scon->chr, buf, size);
+        /* XXX this blocks entire thread. Rewrite to use
+         * qemu_chr_fe_write and background I/O callbacks */
+        qemu_chr_fe_write_all(scon->chr, buf, size);
     }
 }
 
diff --git a/hw/char/sclpconsole.c b/hw/char/sclpconsole.c
index d22464826b..a75ad4f60a 100644
--- a/hw/char/sclpconsole.c
+++ b/hw/char/sclpconsole.c
@@ -168,6 +168,8 @@ static ssize_t write_console_data(SCLPEvent *event, const uint8_t *buf,
         return len;
     }
 
+    /* XXX this blocks entire thread. Rewrite to use
+     * qemu_chr_fe_write and background I/O callbacks */
     return qemu_chr_fe_write_all(scon->chr, buf, len);
 }
 
diff --git a/hw/char/sh_serial.c b/hw/char/sh_serial.c
index 4c55dcb7dc..97ce5629a4 100644
--- a/hw/char/sh_serial.c
+++ b/hw/char/sh_serial.c
@@ -111,7 +111,9 @@ static void sh_serial_write(void *opaque, hwaddr offs,
     case 0x0c: /* FTDR / TDR */
         if (s->chr) {
             ch = val;
-            qemu_chr_fe_write(s->chr, &ch, 1);
+            /* XXX this blocks entire thread. Rewrite to use
+             * qemu_chr_fe_write and background I/O callbacks */
+            qemu_chr_fe_write_all(s->chr, &ch, 1);
 	}
 	s->dr = val;
 	s->flags &= ~SH_SERIAL_FLAG_TDE;
diff --git a/hw/char/spapr_vty.c b/hw/char/spapr_vty.c
index 3498d7b052..9aeafc0c42 100644
--- a/hw/char/spapr_vty.c
+++ b/hw/char/spapr_vty.c
@@ -60,8 +60,9 @@ void vty_putchars(VIOsPAPRDevice *sdev, uint8_t *buf, int len)
 {
     VIOsPAPRVTYDevice *dev = VIO_SPAPR_VTY_DEVICE(sdev);
 
-    /* FIXME: should check the qemu_chr_fe_write() return value */
-    qemu_chr_fe_write(dev->chardev, buf, len);
+    /* XXX this blocks entire thread. Rewrite to use
+     * qemu_chr_fe_write and background I/O callbacks */
+    qemu_chr_fe_write_all(dev->chardev, buf, len);
 }
 
 static void spapr_vty_realize(VIOsPAPRDevice *sdev, Error **errp)
diff --git a/hw/char/stm32f2xx_usart.c b/hw/char/stm32f2xx_usart.c
index 15657abda9..4c6640dbe9 100644
--- a/hw/char/stm32f2xx_usart.c
+++ b/hw/char/stm32f2xx_usart.c
@@ -153,6 +153,8 @@ static void stm32f2xx_usart_write(void *opaque, hwaddr addr,
         if (value < 0xF000) {
             ch = value;
             if (s->chr) {
+                /* XXX this blocks entire thread. Rewrite to use
+                 * qemu_chr_fe_write and background I/O callbacks */
                 qemu_chr_fe_write_all(s->chr, &ch, 1);
             }
             s->usart_sr |= USART_SR_TC;
diff --git a/hw/char/virtio-console.c b/hw/char/virtio-console.c
index 4f0e03d3b7..d44c18c128 100644
--- a/hw/char/virtio-console.c
+++ b/hw/char/virtio-console.c
@@ -68,6 +68,27 @@ static ssize_t flush_buf(VirtIOSerialPort *port,
          */
         if (ret < 0)
             ret = 0;
+
+        /* XXX we should be queuing data to send later for the
+         * console devices too rather than silently dropping
+         * console data on EAGAIN. The Linux virtio-console
+         * hvc driver though does sends with spinlocks held,
+         * so if we enable throttling that'll stall the entire
+         * guest kernel, not merely the process writing to the
+         * console.
+         *
+         * While we could queue data for later write without
+         * enabling throttling, this would result in the guest
+         * being able to trigger arbitrary memory usage in QEMU
+         * buffering data for later writes.
+         *
+         * So fixing this problem likely requires fixing the
+         * Linux virtio-console hvc driver to not hold spinlocks
+         * while writing, and instead merely block the process
+         * that's writing. QEMU would then need some way to detect
+         * if the guest had the fixed driver too, before we can
+         * use throttling on host side.
+         */
         if (!k->is_console) {
             virtio_serial_throttle_port(port, true);
             if (!vcon->watch) {
diff --git a/hw/char/xilinx_uartlite.c b/hw/char/xilinx_uartlite.c
index 4847efb29f..3766dc2c5b 100644
--- a/hw/char/xilinx_uartlite.c
+++ b/hw/char/xilinx_uartlite.c
@@ -144,7 +144,9 @@ uart_write(void *opaque, hwaddr addr,
 
         case R_TX:
             if (s->chr)
-                qemu_chr_fe_write(s->chr, &ch, 1);
+                /* XXX this blocks entire thread. Rewrite to use
+                 * qemu_chr_fe_write and background I/O callbacks */
+                qemu_chr_fe_write_all(s->chr, &ch, 1);
 
             s->regs[addr] = value;