--- a/xen/drivers/char/cadence-uart.c
+++ b/xen/drivers/char/cadence-uart.c
@@ -51,7 +51,7 @@ static void cuart_interrupt(int irq, voi
         /* ACK.  */
         if ( status & UART_SR_INTR_RTRIG )
         {
-            serial_rx_interrupt(port, regs);
+            serial_rx_interrupt(port);
             cuart_write(uart, R_UART_CISR, UART_SR_INTR_RTRIG);
         }
     } while ( status & UART_SR_INTR_RTRIG );
--- a/xen/drivers/char/ehci-dbgp.c
+++ b/xen/drivers/char/ehci-dbgp.c
@@ -1253,6 +1253,7 @@ static void cf_check _ehci_dbgp_poll(str
     unsigned long flags;
     unsigned int timeout = MICROSECS(DBGP_CHECK_INTERVAL);
     bool empty = false;
+    struct cpu_user_regs *old_regs;
 
     if ( !dbgp->ehci_debug )
         return;
@@ -1268,11 +1269,16 @@ static void cf_check _ehci_dbgp_poll(str
         spin_unlock_irqrestore(&port->tx_lock, flags);
     }
 
+    /* Mimic interrupt context. */
+    old_regs = set_irq_regs(regs);
+
     if ( dbgp->in.chunk )
-        serial_rx_interrupt(port, regs);
+        serial_rx_interrupt(port);
 
     if ( empty )
-        serial_tx_interrupt(port, regs);
+        serial_tx_interrupt(port);
+
+    set_irq_regs(old_regs);
 
     if ( spin_trylock_irqsave(&port->tx_lock, flags) )
     {
--- a/xen/drivers/char/exynos4210-uart.c
+++ b/xen/drivers/char/exynos4210-uart.c
@@ -81,7 +81,7 @@ static void exynos4210_uart_interrupt(in
         if ( status & (UINTM_RXD | UINTM_ERROR) )
         {
             /* uart->regs[UINTM] |= RXD|ERROR; */
-            serial_rx_interrupt(port, regs);
+            serial_rx_interrupt(port);
             /* uart->regs[UINTM] &= ~(RXD|ERROR); */
             exynos4210_write(uart, UINTP, UINTM_RXD | UINTM_ERROR);
         }
@@ -89,7 +89,7 @@ static void exynos4210_uart_interrupt(in
         if ( status & (UINTM_TXD | UINTM_MODEM) )
         {
             /* uart->regs[UINTM] |= TXD|MODEM; */
-            serial_tx_interrupt(port, regs);
+            serial_tx_interrupt(port);
             /* uart->regs[UINTM] &= ~(TXD|MODEM); */
             exynos4210_write(uart, UINTP, UINTM_TXD | UINTM_MODEM);
         }
--- a/xen/drivers/char/imx-lpuart.c
+++ b/xen/drivers/char/imx-lpuart.c
@@ -48,10 +48,10 @@ static void imx_lpuart_interrupt(int irq
     rxcnt = imx_lpuart_read(uart, UARTWATER) >> UARTWATER_RXCNT_OFF;
 
     if ( (sts & UARTSTAT_RDRF) || (rxcnt > 0) )
-	    serial_rx_interrupt(port, regs);
+	    serial_rx_interrupt(port);
 
     if ( sts & UARTSTAT_TDRE )
-	    serial_tx_interrupt(port, regs);
+	    serial_tx_interrupt(port);
 
     imx_lpuart_write(uart, UARTSTAT, sts);
 }
--- a/xen/drivers/char/meson-uart.c
+++ b/xen/drivers/char/meson-uart.c
@@ -69,10 +69,10 @@ static void meson_uart_interrupt(int irq
     uint32_t st = readl(uart->regs + AML_UART_STATUS_REG);
 
     if ( !(st & AML_UART_RX_FIFO_EMPTY) )
-        serial_rx_interrupt(port, regs);
+        serial_rx_interrupt(port);
 
     if ( !(st & AML_UART_TX_FIFO_FULL) )
-        serial_tx_interrupt(port, regs);
+        serial_tx_interrupt(port);
 }
 
 static void __init meson_uart_init_preirq(struct serial_port *port)
--- a/xen/drivers/char/mvebu-uart.c
+++ b/xen/drivers/char/mvebu-uart.c
@@ -76,10 +76,10 @@ static void mvebu3700_uart_interrupt(int
 
     if ( st & (STATUS_RX_RDY | STATUS_OVR_ERR | STATUS_FRM_ERR |
                STATUS_BRK_DET) )
-        serial_rx_interrupt(port, regs);
+        serial_rx_interrupt(port);
 
     if ( st & STATUS_TX_RDY )
-        serial_tx_interrupt(port, regs);
+        serial_tx_interrupt(port);
 }
 
 static void __init mvebu3700_uart_init_preirq(struct serial_port *port)
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -188,9 +188,9 @@ static void cf_check ns16550_interrupt(
         u8 lsr = ns_read_reg(uart, UART_LSR);
 
         if ( (lsr & uart->lsr_mask) == uart->lsr_mask )
-            serial_tx_interrupt(port, regs);
+            serial_tx_interrupt(port);
         if ( lsr & UART_LSR_DR )
-            serial_rx_interrupt(port, regs);
+            serial_rx_interrupt(port);
 
         /* A "busy-detect" condition is observed on Allwinner/sunxi UART
          * after LCR is written during setup. It needs to be cleared at
@@ -211,22 +211,27 @@ static void cf_check __ns16550_poll(stru
 {
     struct serial_port *port = this_cpu(poll_port);
     struct ns16550 *uart = port->uart;
+    struct cpu_user_regs *old_regs;
 
     if ( uart->intr_works )
         return; /* Interrupts work - no more polling */
 
+    /* Mimic interrupt context. */
+    old_regs = set_irq_regs(regs);
+
     while ( ns_read_reg(uart, UART_LSR) & UART_LSR_DR )
     {
         if ( ns16550_ioport_invalid(uart) )
             goto out;
 
-        serial_rx_interrupt(port, regs);
+        serial_rx_interrupt(port);
     }
 
     if ( ( ns_read_reg(uart, UART_LSR) & uart->lsr_mask ) == uart->lsr_mask )
-        serial_tx_interrupt(port, regs);
+        serial_tx_interrupt(port);
 
 out:
+    set_irq_regs(old_regs);
     set_timer(&uart->timer, NOW() + MILLISECS(uart->timeout_ms));
 }
 
--- a/xen/drivers/char/omap-uart.c
+++ b/xen/drivers/char/omap-uart.c
@@ -70,9 +70,9 @@ static void omap_uart_interrupt(int irq,
     {
         lsr = omap_read(uart, UART_LSR) & 0xff;
 	if ( lsr & UART_LSR_THRE )
-            serial_tx_interrupt(port, regs);
+            serial_tx_interrupt(port);
 	if ( lsr & UART_LSR_DR )
-            serial_rx_interrupt(port, regs);
+            serial_rx_interrupt(port);
 
         if ( port->txbufc == port->txbufp ) {
             reg = omap_read(uart, UART_IER);
--- a/xen/drivers/char/pl011.c
+++ b/xen/drivers/char/pl011.c
@@ -95,7 +95,7 @@ static void pl011_interrupt(int irq, voi
             pl011_write(uart, ICR, status & ~(TXI|RTI|RXI));
 
             if ( status & (RTI|RXI) )
-                serial_rx_interrupt(port, regs);
+                serial_rx_interrupt(port);
 
             /* TODO
                 if ( status & (DSRMI|DCDMI|CTSMI|RIMI) )
@@ -103,7 +103,7 @@ static void pl011_interrupt(int irq, voi
             */
 
             if ( status & (TXI) )
-                serial_tx_interrupt(port, regs);
+                serial_tx_interrupt(port);
 
             status = pl011_intr_status(uart);
         } while (status != 0);
--- a/xen/drivers/char/scif-uart.c
+++ b/xen/drivers/char/scif-uart.c
@@ -119,11 +119,11 @@ static void scif_uart_interrupt(int irq,
     {
         /* TX Interrupt */
         if ( status & SCFSR_TDFE )
-            serial_tx_interrupt(port, regs);
+            serial_tx_interrupt(port);
 
         /* RX Interrupt */
         if ( status & (SCFSR_RDF | SCFSR_DR) )
-            serial_rx_interrupt(port, regs);
+            serial_rx_interrupt(port);
 
         /* Error Interrupt */
         if ( status & params->error_mask )
--- a/xen/drivers/char/serial.c
+++ b/xen/drivers/char/serial.c
@@ -45,7 +45,7 @@ static inline void serial_stop_tx(struct
         port->driver->stop_tx(port);
 }
 
-void serial_rx_interrupt(struct serial_port *port, struct cpu_user_regs *regs)
+void serial_rx_interrupt(struct serial_port *port)
 {
     char c;
     serial_rx_fn fn = NULL;
@@ -71,7 +71,7 @@ void serial_rx_interrupt(struct serial_p
         fn(c & 0x7f);
 }
 
-void serial_tx_interrupt(struct serial_port *port, struct cpu_user_regs *regs)
+void serial_tx_interrupt(struct serial_port *port)
 {
     int i, n;
     unsigned long flags;
--- a/xen/drivers/char/xhci-dbc.c
+++ b/xen/drivers/char/xhci-dbc.c
@@ -1164,6 +1164,7 @@ static void cf_check dbc_uart_poll(void
     struct dbc_uart *uart = port->uart;
     struct dbc *dbc = &uart->dbc;
     unsigned long flags = 0;
+    struct cpu_user_regs *old_regs;
 
     if ( spin_trylock_irqsave(&port->tx_lock, flags) )
     {
@@ -1175,10 +1176,15 @@ static void cf_check dbc_uart_poll(void
         spin_unlock_irqrestore(&port->tx_lock, flags);
     }
 
+    /* Mimic interrupt context. */
+    old_regs = set_irq_regs(guest_cpu_user_regs());
+
     while ( dbc_work_ring_size(&dbc->dbc_iwork) )
-        serial_rx_interrupt(port, guest_cpu_user_regs());
+        serial_rx_interrupt(port);
+
+    serial_tx_interrupt(port);
 
-    serial_tx_interrupt(port, guest_cpu_user_regs());
+    set_irq_regs(old_regs);
     set_timer(&uart->timer, NOW() + MICROSECS(DBC_POLL_INTERVAL));
 }
 
--- a/xen/include/xen/serial.h
+++ b/xen/include/xen/serial.h
@@ -12,8 +12,6 @@
 #include <xen/init.h>
 #include <xen/spinlock.h>
 
-struct cpu_user_regs;
-
 /* Register a character-receive hook on the specified COM port. */
 typedef void (*serial_rx_fn)(char c);
 void serial_set_rx_handler(int handle, serial_rx_fn fn);
@@ -155,8 +153,8 @@ void serial_register_uart(int idx, struc
 /* Place the serial port into asynchronous transmit mode. */
 void serial_async_transmit(struct serial_port *port);
 /* Process work in interrupt context. */
-void serial_rx_interrupt(struct serial_port *port, struct cpu_user_regs *regs);
-void serial_tx_interrupt(struct serial_port *port, struct cpu_user_regs *regs);
+void serial_rx_interrupt(struct serial_port *port);
+void serial_tx_interrupt(struct serial_port *port);
 
 /*
  * Initialisers for individual uart drivers.
