Re: [Xen-devel] [PATCH 03/14 v4] xen/arm: vpl011: Add pl011 uart emulation in Xen

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

On 06/06/17 18:25, Bhupinder Thakur wrote:
> Add emulation code to emulate read/write access to pl011 registers
> and pl011 interrupts:
> 
>     - Emulate DR read/write by reading and writing from/to the IN
>       and OUT ring buffers and raising an event to the backend when
>       there is data in the OUT ring buffer and injecting an interrupt
>       to the guest when there is data in the IN ring buffer
> 
>     - Other registers are related to interrupt management and
>       essentially control when interrupts are delivered to the guest
> 
> The SBSA compliant pl011 uart is covered in Appendix B of
> https://static.docs.arm.com/den0029/a/Server_Base_System_Architecture_v3_1_ARM_DEN_0029A.pdf
> 
> Signed-off-by: Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>
> ---
> CC: ij
> CC: wl
> CC: ss
> CC: jg
> CC: kw
> 
> Changes since v3:
> - Moved the call to DEFINE_XEN_FLEX_RING from vpl011.h to public/console.h. 
> This macro defines
>   standard functions to operate on the ring buffer.
> - Lock taken while updating the interrupt mask and clear registers in 
> mmio_write.
> - Use gfn_t instead of xen_pfn_t.
> - vgic_free_virq called if there is any error in vpl011 initialization.
> - mmio handlers freed if there is any error in vpl011 initialization.
> - Removed vpl011->initialized flag usage as the same check could be done 
>   using vpl011->ring-ref.
> - Used return instead of break in the switch handling of emulation of 
> different pl011 registers.
> - Renamed vpl011_update_spi() to vpl011_update().
> 
> Changes since v2:
> - Use generic vreg_reg* for read/write of registers emulating pl011.
> - Use generic ring buffer functions defined using DEFINE_XEN_FLEX_RING.
> - Renamed the SPI injection function to vpl011_update_spi() to reflect level 
>   triggered nature of pl011 interrupts.
> - The pl011 register access address should always be the base address of the
>   corresponding register as per section B of the SBSA document. For this 
> reason,
>   the register range address access is not allowed.
> 
> Changes since v1:
> - Removed the optimiztion related to sendiing events to xenconsole 
> - Use local variables as ring buffer indices while using the ring buffer
> 
>  tools/console/daemon/io.c        |   2 +-
>  xen/arch/arm/Kconfig             |   5 +
>  xen/arch/arm/Makefile            |   1 +
>  xen/arch/arm/vpl011.c            | 418 
> +++++++++++++++++++++++++++++++++++++++
>  xen/include/asm-arm/domain.h     |   6 +
>  xen/include/asm-arm/pl011-uart.h |   2 +
>  xen/include/asm-arm/vpl011.h     |  74 +++++++
>  xen/include/public/arch-arm.h    |   6 +
>  xen/include/public/io/console.h  |   4 +
>  9 files changed, 517 insertions(+), 1 deletion(-)
>  create mode 100644 xen/arch/arm/vpl011.c
>  create mode 100644 xen/include/asm-arm/vpl011.h
> 
> diff --git a/tools/console/daemon/io.c b/tools/console/daemon/io.c
> index 7e6a886..947f13a 100644
> --- a/tools/console/daemon/io.c
> +++ b/tools/console/daemon/io.c
> @@ -21,6 +21,7 @@
>  
>  #include "utils.h"
>  #include "io.h"
> +#include <string.h>
>  #include <xenevtchn.h>
>  #include <xengnttab.h>
>  #include <xenstore.h>
> @@ -29,7 +30,6 @@
>  
>  #include <stdlib.h>
>  #include <errno.h>
> -#include <string.h>
>  #include <poll.h>
>  #include <fcntl.h>
>  #include <unistd.h>
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index d46b98c..c1a0e7f 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -50,6 +50,11 @@ config HAS_ITS
>          prompt "GICv3 ITS MSI controller support" if EXPERT = "y"
>          depends on HAS_GICV3
>  
> +config VPL011_CONSOLE
> +     bool "Emulated pl011 console support"
> +     default y
> +     ---help---
> +       Allows a guest to use pl011 UART as a console

I admit that I am rather late with this comment, but I am not sure we
should advertise PL011 emulation here.
Technically what you emulate is a "SBSA Generic UART", which is indeed a
subset of the PL011, but really only a subset. You confirm this already
in patch 13/14, where you use the respective compatible name instead of
the generic arm,pl011 one.

So while I don't dare to ask for renaming every identifier, I wonder if
we should at least keep the publicly visible part confined to "SBSA
UART". You could mention the subset nature in the help message here, for
instance.
The same reasoning applies to other parts of this series which introduce
user-visible strings (like in libxl).

>  endmenu
>  
>  menu "ARM errata workaround via the alternative framework"
> diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
> index 49e1fb2..15efc13 100644
> --- a/xen/arch/arm/Makefile
> +++ b/xen/arch/arm/Makefile
> @@ -52,6 +52,7 @@ obj-y += vm_event.o
>  obj-y += vtimer.o
>  obj-y += vpsci.o
>  obj-y += vuart.o
> +obj-$(CONFIG_VPL011_CONSOLE) += vpl011.o
>  
>  #obj-bin-y += ....o
>  
> diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
> new file mode 100644
> index 0000000..9b1f27e
> --- /dev/null
> +++ b/xen/arch/arm/vpl011.c
> @@ -0,0 +1,418 @@
> +/*
> + * arch/arm/vpl011.c
> + *
> + * Virtual PL011 UART
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along 
> with
> + * this program; If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <xen/errno.h>
> +#include <xen/event.h>
> +#include <xen/guest_access.h>
> +#include <xen/init.h>
> +#include <xen/lib.h>
> +#include <xen/mm.h>
> +#include <xen/sched.h>
> +#include <public/domctl.h>
> +#include <public/io/console.h>
> +#include <asm-arm/pl011-uart.h>
> +#include <asm-arm/vgic-emul.h>
> +#include <asm-arm/vpl011.h>

I think Julien mentioned this already, but I think you should just use
"#include <asm/.. .h>" here.

> +
> +static bool vpl011_reg32_check_access(struct hsr_dabt dabt)
> +{
> +    return (dabt.size != DABT_DOUBLE_WORD);
> +}
> +
> +static void vpl011_update(struct domain *d)

Can you please rename this function to indicate that it updates the
*interrupt status*? That name as it is rather generic at the moment.

> +{
> +    struct vpl011 *vpl011 = &d->arch.vpl011;
> +
> +    /*
> +     * TODO: PL011 interrupts are level triggered which means
> +     * that interrupt needs to be set/clear instead of being
> +     * injected. However, currently vGIC does not handle level 
> +     * triggered interrupts properly. This function needs to be 
> +     * revisited once vGIC starts handling level triggered 
> +     * interrupts.
> +     */
> +    if ( vpl011->uartris & vpl011->uartimsc )
> +        vgic_vcpu_inject_spi(d, GUEST_VPL011_SPI);

So my understanding is that this is using an edge triggered semantic at
the moment. While this is not what an PL011 actually implements and not
what the driver really expects, this is fine on itself for now.
BUT I think we may want to avoid injecting spurious interrupts now:
If for instance the receive interrupt condition is set and we clear the
transmit interrupt bit, then call this function, it would inject a new
interrupt, although in a edge-triggered world we really wouldn't need to
do anything.
So I believe we would need to have some kind of shadowed interrupt
state, which stores the interrupt condition the guest already knows
about. As soon as we *add* a bit to this state, we inject the SPI.
This would act as a kind of temporary bridge between the level triggered
SBSA/PL011 UART and the edge-only VGIC implementation for now.
Later when the VGIC properly handles level triggered interrupts, this
implementation can be adjusted. But this change should then be confined
to this very function.

> +}
> +
> +static uint8_t vpl011_read_data(struct domain *d)
> +{
> +    unsigned long flags;
> +    uint8_t data = 0;
> +    struct vpl011 *vpl011 = &d->arch.vpl011;
> +    struct xencons_interface *intf = vpl011->ring_buf;
> +    XENCONS_RING_IDX in_cons = intf->in_cons;
> +    XENCONS_RING_IDX in_prod = intf->in_prod;
> +
> +    VPL011_LOCK(d, flags);
> +
> +    /*
> +     * It is expected that there will be data in the ring buffer when this
> +     * function is called since the guest is expected to read the data 
> register
> +     * only if the TXFE flag is not set.
> +     * If the guest still does read when TXFE bit is set then 0 will be 
> returned.
> +     */
> +    if ( xencons_queued(in_prod, in_cons, sizeof(intf->in)) > 0 )
> +    {
> +        data = intf->in[xencons_mask(in_cons, sizeof(intf->in))];
> +        in_cons += 1;
> +        intf->in_cons = in_cons;
> +        smp_mb();
> +    }
> +    else
> +    {
> +        gprintk(XENLOG_ERR, "vpl011: Unexpected IN ring buffer empty\n");
> +    }
> +
> +    if ( xencons_queued(in_prod, in_cons, sizeof(intf->in)) == 0 )
> +    {
> +        vpl011->uartfr |= RXFE;
> +        vpl011->uartris &= ~RXI;

In a level triggered world you would need to possibly change the status
of the interrupt line here, so a call to (a renamed and fixed)
vpl011_update() function would be due here. To make the transition later
as easy as possible, I'd recommend to implement this shadow interrupt
state as described above and then call the interrupt update function
here already.

> +    }
> +    vpl011->uartfr &= ~RXFF;
> +    VPL011_UNLOCK(d, flags);
> +
> +    return data;
> +}
> +
> +static void vpl011_write_data(struct domain *d, uint8_t data)
> +{
> +    unsigned long flags;
> +    struct vpl011 *vpl011 = &d->arch.vpl011;
> +    struct xencons_interface *intf = vpl011->ring_buf;
> +    XENCONS_RING_IDX out_cons = intf->out_cons;
> +    XENCONS_RING_IDX out_prod = intf->out_prod;
> +
> +    VPL011_LOCK(d, flags);
> +
> +    /*
> +     * It is expected that the ring is not full when this function is called
> +     * as the guest is expected to write to the data register only when the
> +     * TXFF flag is not set.
> +     * In case the guest does write even when the TXFF flag is set then the
> +     * data will be silently dropped.
> +     */
> +    if ( xencons_queued(out_prod, out_cons, sizeof(intf->out)) !=
> +         sizeof (intf->out) )
> +    {
> +        intf->out[xencons_mask(out_prod, sizeof(intf->out))] = data;
> +        smp_wmb();
> +        out_prod += 1;
> +        intf->out_prod = out_prod;
> +    }
> +    else
> +    {
> +        gprintk(XENLOG_ERR, "vpl011: Unexpected OUT ring buffer full\n");
> +    }
> +
> +    if ( xencons_queued(out_prod, out_cons, sizeof(intf->out)) ==
> +         sizeof (intf->out) )
> +    {
> +        vpl011->uartfr |= TXFF;
> +        vpl011->uartris &= ~TXI;

Same as above. Basically whenever you change one of the bits that may
affect the status of the interrupt line, I'd call the update function.

> +    }
> +
> +    vpl011->uartfr |= BUSY;
> +
> +    vpl011->uartfr &= ~TXFE;
> +
> +    VPL011_UNLOCK(d, flags);
> +
> +    /*
> +     * Send an event to console backend to indicate that there is 
> +     * data in the OUT ring buffer.
> +     */
> +    notify_via_xen_event_channel(d, vpl011->evtchn);
> +}
> +
> +static int vpl011_mmio_read(struct vcpu *v,
> +                            mmio_info_t *info,
> +                            register_t *r,
> +                            void *priv)
> +{
> +    struct hsr_dabt dabt = info->dabt;
> +    uint32_t vpl011_reg = (uint32_t)(info->gpa - GUEST_PL011_BASE);
> +    struct vpl011 *vpl011 = &v->domain->arch.vpl011;
> +
> +    switch ( vpl011_reg )
> +    {
> +    case DR:
> +        /*
> +         * Since pl011 registers are 32-bit registers, all registers
> +         * are handled similarly allowing 8-bit, 16-bit and 32-bit
> +         * accesses.
> +         */
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        *r = vreg_reg32_extract(vpl011_read_data(v->domain), info);
> +        return 1;
> +
> +    case RSR:
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        /* It always returns 0 as there are no physical errors. */
> +        *r = 0;
> +        return 1;
> +
> +    case FR:
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        *r = vreg_reg32_extract(vpl011->uartfr, info);
> +        return 1;
> +
> +    case RIS:
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        *r = vreg_reg32_extract(vpl011->uartris, info);
> +        return 1;
> +
> +    case MIS:
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        *r = vreg_reg32_extract(vpl011->uartris & 
> +                                vpl011->uartimsc, info);

That smells like you need a lock here, since another access could change
either RIS and/or IMSC concurrently.
But as Julien already mentioned, these accesses are prone to races
anyway, since vreg_reg32_extract() is not atomic.
So is it worth to take the lock here just before the whole switch statement?

> +        return 1;
> +
> +    case IMSC:
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        *r = vreg_reg32_extract(vpl011->uartimsc, info);
> +        return 1;
> +
> +    case ICR:
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        /* Only write is valid. */
> +        return 0;
> +
> +    default:
> +        gprintk(XENLOG_ERR, "vpl011: unhandled read r%d offset %#08x\n",
> +                dabt.reg, vpl011_reg);
> +        return 0;
> +    }
> +
> +    return 1;
> +
> +bad_width:
> +    gprintk(XENLOG_ERR, "vpl011: bad read width %d r%d offset %#08x\n",
> +            dabt.size, dabt.reg, vpl011_reg);
> +    domain_crash_synchronous();
> +    return 0;
> +
> +}
> +
> +static int vpl011_mmio_write(struct vcpu *v,
> +                             mmio_info_t *info,
> +                             register_t r,
> +                             void *priv)
> +{
> +    struct hsr_dabt dabt = info->dabt;
> +    uint32_t vpl011_reg = (uint32_t)(info->gpa - GUEST_PL011_BASE);
> +    struct vpl011 *vpl011 = &v->domain->arch.vpl011;
> +    struct domain *d = v->domain;
> +    unsigned long flags;
> +
> +    switch ( vpl011_reg )
> +    {
> +    case DR:
> +    {
> +        uint32_t data = 0;
> +
> +        /*
> +         * Since pl011 registers are 32-bit registers, all registers
> +         * are handled similarly allowing 8-bit, 16-bit and 32-bit
> +         * accesses.
> +         */
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        vreg_reg32_update(&data, r, info);
> +        data &= 0xFF;

This is not needed as vpl011_write_data()'s second argument is uint8_t,
so the compiler does this masking anyway.
And even if it wouldn't, you could move this statement into the call.

> +        vpl011_write_data(v->domain, data);
> +        return 1;
> +    }
> +    case RSR: /* Nothing to clear. */
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        return 1; 
> +
> +    case FR:
> +    case RIS:
> +    case MIS:
> +        goto write_ignore;
> +
> +    case IMSC:
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        VPL011_LOCK(d, flags);
> +        vreg_reg32_update(&vpl011->uartimsc, r, info);
> +        VPL011_UNLOCK(d, flags);
> +        vpl011_update(v->domain);
> +        return 1;
> +
> +    case ICR:
> +        if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> +
> +        VPL011_LOCK(d, flags);
> +        vreg_reg32_clearbits(&vpl011->uartris, r, info);

Please call the interrupt status update function here.

> +        VPL011_UNLOCK(d, flags);
> +        vpl011_update(d);
> +        return 1;
> +
> +    default:
> +        gprintk(XENLOG_ERR, "vpl011: unhandled write r%d offset %#08x\n",
> +                dabt.reg, vpl011_reg);
> +        return 0;
> +    }
> +
> +write_ignore:
> +    return 1;
> +
> +bad_width:
> +    gprintk(XENLOG_ERR, "vpl011: bad write width %d r%d offset %#08x\n",
> +            dabt.size, dabt.reg, vpl011_reg);
> +    domain_crash_synchronous();
> +    return 0;
> +
> +}
> +
> +static const struct mmio_handler_ops vpl011_mmio_handler = {
> +    .read = vpl011_mmio_read,
> +    .write = vpl011_mmio_write,
> +};
> +
> +static void vpl011_data_avail(struct domain *d)
> +{
> +    unsigned long flags;
> +    struct vpl011 *vpl011 = &d->arch.vpl011;
> +    struct xencons_interface *intf = vpl011->ring_buf;
> +    XENCONS_RING_IDX in_cons = intf->in_cons;
> +    XENCONS_RING_IDX in_prod = intf->in_prod;
> +    XENCONS_RING_IDX out_cons = intf->out_cons;
> +    XENCONS_RING_IDX out_prod = intf->out_prod;
> +    XENCONS_RING_IDX in_ring_qsize, out_ring_qsize;
> +
> +    VPL011_LOCK(d, flags);
> +
> +    in_ring_qsize = xencons_queued(in_prod,
> +                                   in_cons,
> +                                   sizeof(intf->in));
> +
> +    out_ring_qsize = xencons_queued(out_prod,
> +                                    out_cons,
> +                                    sizeof(intf->out));
> +
> +    /* Update the uart rx state if the buffer is not empty. */
> +    if ( in_ring_qsize != 0 )
> +    {
> +        vpl011->uartfr &= ~RXFE;
> +        if ( in_ring_qsize == sizeof(intf->in) )
> +            vpl011->uartfr |= RXFF;
> +        vpl011->uartris |= RXI;

... and here ...

> +    }
> +
> +    /* Update the uart tx state if the buffer is not full. */
> +    if ( out_ring_qsize != sizeof(intf->out) )
> +    {
> +        vpl011->uartfr &= ~TXFF;
> +        vpl011->uartris |= TXI;

... and here.

I didn't look at the locking issue on the Xen console for now, but might
join this discussion later.

Cheers,
Andre.

> +        if ( out_ring_qsize == 0 )
> +        {
> +            vpl011->uartfr &= ~BUSY;
> +            vpl011->uartfr |= TXFE;
> +        }
> +    }
> +
> +    VPL011_UNLOCK(d, flags);
> +
> +    vpl011_update(d);
> +}
> +
> +
> +static void vpl011_notification(struct vcpu *v, unsigned int port)
> +{
> +    vpl011_data_avail(v->domain);
> +}
> +
> +int domain_vpl011_init(struct domain *d, struct vpl011_init_info *info)
> +{
> +    int rc;
> +    struct vpl011 *vpl011 = &d->arch.vpl011;
> +
> +    if ( vpl011->ring_buf )
> +        return 0;
> +
> +    /* Map the guest PFN to Xen address space. */
> +    rc =  prepare_ring_for_helper(d,
> +                                  gfn_x(info->gfn),
> +                                  &vpl011->ring_page,
> +                                  &vpl011->ring_buf);
> +    if ( rc < 0 )
> +        goto out;
> +
> +    rc = vgic_reserve_virq(d, GUEST_VPL011_SPI);
> +    if ( !rc )
> +    {
> +        rc = -EINVAL;
> +        goto out1;
> +    }
> +
> +    register_mmio_handler(d, &vpl011_mmio_handler,
> +                          GUEST_PL011_BASE, GUEST_PL011_SIZE, NULL);
> +
> +    spin_lock_init(&vpl011->lock);
> +
> +    rc = alloc_unbound_xen_event_channel(d, 0, info->console_domid,
> +                                         vpl011_notification);
> +    if ( rc < 0 )
> +        goto out2;
> +
> +    vpl011->evtchn = info->evtchn = rc;
> +
> +    return 0;
> +
> +out2:
> +    xfree(d->arch.vmmio.handlers);
> +    vgic_free_virq(d, GUEST_VPL011_SPI);
> +
> +out1:
> +    destroy_ring_for_helper(&vpl011->ring_buf, vpl011->ring_page);
> +
> +out:
> +    return rc;
> +}
> +
> +void domain_vpl011_deinit(struct domain *d)
> +{
> +    struct vpl011 *vpl011 = &d->arch.vpl011;
> +
> +    if ( !vpl011->ring_buf )
> +        return;
> +
> +    free_xen_event_channel(d, vpl011->evtchn);
> +    destroy_ring_for_helper(&vpl011->ring_buf, vpl011->ring_page);
> +    xfree(d->arch.vmmio.handlers);
> +}
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
> index 6de8082..91d1061 100644
> --- a/xen/include/asm-arm/domain.h
> +++ b/xen/include/asm-arm/domain.h
> @@ -11,6 +11,7 @@
>  #include <public/hvm/params.h>
>  #include <xen/serial.h>
>  #include <xen/rbtree.h>
> +#include <asm-arm/vpl011.h>
>  
>  struct hvm_domain
>  {
> @@ -133,6 +134,11 @@ struct arch_domain
>      struct {
>          uint8_t privileged_call_enabled : 1;
>      } monitor;
> +
> +#ifdef CONFIG_VPL011_CONSOLE
> +    struct vpl011 vpl011;
> +#endif
> +
>  }  __cacheline_aligned;
>  
>  struct arch_vcpu
> diff --git a/xen/include/asm-arm/pl011-uart.h 
> b/xen/include/asm-arm/pl011-uart.h
> index 123f477..57e9ec7 100644
> --- a/xen/include/asm-arm/pl011-uart.h
> +++ b/xen/include/asm-arm/pl011-uart.h
> @@ -49,6 +49,8 @@
>  /* FR bits */
>  #define TXFE   (1<<7) /* TX FIFO empty */
>  #define RXFE   (1<<4) /* RX FIFO empty */
> +#define TXFF   (1<<5) /* TX FIFO full */
> +#define RXFF   (1<<6) /* RX FIFO full */
>  #define BUSY   (1<<3) /* Transmit is not complete */
>  
>  /* LCR_H bits */
> diff --git a/xen/include/asm-arm/vpl011.h b/xen/include/asm-arm/vpl011.h
> new file mode 100644
> index 0000000..b3e332d
> --- /dev/null
> +++ b/xen/include/asm-arm/vpl011.h
> @@ -0,0 +1,74 @@
> +/*
> + * include/xen/vpl011.h
> + *
> + * Virtual PL011 UART
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along 
> with
> + * this program; If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef _VPL011_H_
> +
> +#define _VPL011_H_
> +
> +#include <public/domctl.h>
> +#include <public/io/ring.h>
> +#include <asm-arm/vreg.h>
> +#include <xen/mm.h>
> +
> +/* helper macros */
> +#define VPL011_LOCK(d,flags) spin_lock_irqsave(&(d)->arch.vpl011.lock, flags)
> +#define VPL011_UNLOCK(d,flags) 
> spin_unlock_irqrestore(&(d)->arch.vpl011.lock, flags)
> +
> +struct vpl011 {
> +    void *ring_buf;
> +    struct page_info *ring_page;
> +    uint32_t    uartfr;     /* Flag register */
> +    uint32_t    uartcr;     /* Control register */
> +    uint32_t    uartimsc;   /* Interrupt mask register*/
> +    uint32_t    uarticr;    /* Interrupt clear register */
> +    uint32_t    uartris;    /* Raw interrupt status register */
> +    uint32_t    uartmis;    /* Masked interrupt register */
> +    spinlock_t  lock;
> +    evtchn_port_t evtchn;
> +};
> +
> +struct vpl011_init_info {
> +    uint32_t console_domid;
> +    gfn_t gfn;
> +    evtchn_port_t evtchn;
> +};
> +
> +#ifdef CONFIG_VPL011_CONSOLE
> +int domain_vpl011_init(struct domain *d,
> +                       struct vpl011_init_info *info);
> +void domain_vpl011_deinit(struct domain *d);
> +#else
> +static inline int domain_vpl011_init(struct domain *d,
> +                                     struct vpl011_init_info *info)
> +{
> +    return -ENOSYS;
> +}
> +
> +static inline void domain_vpl011_deinit(struct domain *d) { }
> +#endif
> +
> +#endif
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
> index bd974fb..85ab665 100644
> --- a/xen/include/public/arch-arm.h
> +++ b/xen/include/public/arch-arm.h
> @@ -410,6 +410,10 @@ typedef uint64_t xen_callback_t;
>  #define GUEST_ACPI_BASE 0x20000000ULL
>  #define GUEST_ACPI_SIZE 0x02000000ULL
>  
> +/* PL011 mappings */
> +#define GUEST_PL011_BASE    0x22000000ULL
> +#define GUEST_PL011_SIZE    0x00001000ULL
> +
>  /*
>   * 16MB == 4096 pages reserved for guest to use as a region to map its
>   * grant table in.
> @@ -444,6 +448,8 @@ typedef uint64_t xen_callback_t;
>  #define GUEST_TIMER_PHYS_NS_PPI 30
>  #define GUEST_EVTCHN_PPI        31
>  
> +#define GUEST_VPL011_SPI        32
> +
>  /* PSCI functions */
>  #define PSCI_cpu_suspend 0
>  #define PSCI_cpu_off     1
> diff --git a/xen/include/public/io/console.h b/xen/include/public/io/console.h
> index e2cd97f..5e45e1c 100644
> --- a/xen/include/public/io/console.h
> +++ b/xen/include/public/io/console.h
> @@ -27,6 +27,8 @@
>  #ifndef __XEN_PUBLIC_IO_CONSOLE_H__
>  #define __XEN_PUBLIC_IO_CONSOLE_H__
>  
> +#include "ring.h"
> +
>  typedef uint32_t XENCONS_RING_IDX;
>  
>  #define MASK_XENCONS_IDX(idx, ring) ((idx) & (sizeof(ring)-1))
> @@ -38,6 +40,8 @@ struct xencons_interface {
>      XENCONS_RING_IDX out_cons, out_prod;
>  };
>  
> +DEFINE_XEN_FLEX_RING(xencons);
> +
>  #endif /* __XEN_PUBLIC_IO_CONSOLE_H__ */
>  
>  /*
> 

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