Re: [Xen-devel] [PATCH 01/10] xen/arm: vpl011: Add pl011 uart emulation in Xen

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 3 Apr 2017, 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>
> ---
>  xen/arch/arm/Kconfig             |   5 +
>  xen/arch/arm/Makefile            |   1 +
>  xen/arch/arm/vpl011.c            | 339 
> +++++++++++++++++++++++++++++++++++++++
>  xen/include/asm-arm/domain.h     |   5 +
>  xen/include/asm-arm/pl011-uart.h |   2 +
>  xen/include/public/arch-arm.h    |   8 +
>  xen/include/xen/vpl011.h         |  67 ++++++++
>  7 files changed, 427 insertions(+)
>  create mode 100644 xen/arch/arm/vpl011.c
>  create mode 100644 xen/include/xen/vpl011.h
> 
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index 2e023d1..bfa86c7 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -45,6 +45,11 @@ config ACPI
>  config HAS_GICV3
>       bool
>  
> +config VPL011_CONSOLE
> +     bool "Emulated pl011 console support"
> +     default y
> +     ---help---
> +       Allows a guest to use pl011 UART as a console
>  endmenu
>  
>  menu "ARM errata workaround via the alternative framework"
> diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
> index 7afb8a3..a94bdab 100644
> --- a/xen/arch/arm/Makefile
> +++ b/xen/arch/arm/Makefile
> @@ -49,6 +49,7 @@ 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..eeb1cbf
> --- /dev/null
> +++ b/xen/arch/arm/vpl011.c
> @@ -0,0 +1,339 @@
> +/*
> + * 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/init.h>
> +#include <xen/lib.h>
> +#include <xen/errno.h>
> +#include <xen/guest_access.h>
> +#include <xen/sched.h>
> +#include <xen/event.h>
> +#include <public/io/console.h>
> +#include <xen/vpl011.h>
> +#include <asm-arm/pl011-uart.h>
> +
> +unsigned int vpl011_reg_mask[] = {0xff, 0xffff, 0xffffffff};
> +
> +static void vgic_inject_vpl011_spi(struct domain *d)
> +{
> +    struct vpl011_s *vpl011=&d->arch.vpl011;
> +
> +    if ( (vpl011->uartris & vpl011->uartimsc) )
> +        vgic_vcpu_inject_spi(d, GUEST_VPL011_SPI);
> +}
> +
> +static void vpl011_read_data(struct domain *d, uint8_t *data)
> +{
> +    unsigned long flags;
> +    struct vpl011_s *vpl011=&d->arch.vpl011;

The code style is:
    
    vpl011 = &d->arch.vpl011


> +    struct xencons_interface *intf=(struct xencons_interface 
> *)vpl011->ring_buf;

Same here. Please fix it everywhere.


> +    /*
> +     * Initialize the data so that even if there is no data in ring buffer
> +     * 0 is returned.
> +     */
> +    *data = 0;
> +
> +    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 event when TXFE bit is set then 0 will
> +     * be returned.
> +     */
> +    if ( !VPL011_IN_RING_EMPTY(intf) )
> +    {
> +        *data = intf->in[MASK_XENCONS_IDX(intf->in_cons++, intf->in)];

For correctness, it is important to maintain the right ordering and use
barriers:

        in_cons = intf->in_cons;
        *data = intf->in[MASK_XENCONS_IDX(in_cons, intf->in)];
        smb_mb();
        intf->in_cons = in_cons + 1;


> +    }
> +
> +    if ( VPL011_IN_RING_EMPTY(intf) )
> +    {
> +        vpl011->uartfr |= (RXFE);
> +        vpl011->uartris &= ~(RXI);
> +    }
> +
> +    vpl011->uartfr &= ~(RXFF);
> +
> +    VPL011_UNLOCK(d, flags);

I think we need to notify xenconsoled here, in case the ring was
previosuly full? Now that we have read some data, xenconsoled can go
back and write more.


> +}
> +
> +static void vpl011_write_data(struct domain *d, uint8_t data)
> +{
> +    unsigned long flags;
> +    struct vpl011_s *vpl011=&d->arch.vpl011;
> +    struct xencons_interface *intf=(struct xencons_interface 
> *)vpl011->ring_buf;
> +
> +    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 ( !VPL011_OUT_RING_FULL(intf) )
> +    {
> +        intf->out[MASK_XENCONS_IDX(intf->out_prod++, intf->out)] = data;
> +        smp_wmb();

Similarly, the order should be:

    out_prod = intf->out_prod;
    intf->out[MASK_XENCONS_IDX(out_prod, intf->out)] = data;
    smb_wmb();
    intf->out_prod = out_prod + 1;


> +    }
> +
> +    if ( VPL011_OUT_RING_FULL(intf) )
> +    {
> +        vpl011->uartfr |= (TXFF);
> +        vpl011->uartris &= ~(TXI);
> +    }
> +
> +    vpl011->uartfr |= (BUSY);
> +
> +    vpl011->uartfr &= ~(TXFE);
> +
> +    VPL011_UNLOCK(d, flags);
> +
> +    /* raise an event to xenconsoled only if it is the first character in 
> the buffer */
> +    if ( VPL011_RING_DEPTH(intf, out) == 1 )
> +    {
> +        notify_via_xen_event_channel(d, 
> d->arch.hvm_domain.params[HVM_PARAM_VCONSOLE_EVTCHN]);
> +    }

Why only in case is the first character? xenconsoled will miss updates
if we don't send a notification, right?


> +}
> +
> +static int vpl011_mmio_read(struct vcpu *v, mmio_info_t *info, register_t 
> *r, void *priv)
> +{
> +    uint8_t ch;
> +    struct hsr_dabt dabt = info->dabt;
> +    int vpl011_reg = (int)(info->gpa - GUEST_PL011_BASE);
> +    struct vpl011_s *vpl011 = &v->domain->arch.vpl011;
> +
> +    switch ( vpl011_reg )
> +    {
> +    case DR:
> +        if ( !VALID_W_SIZE(dabt.size) ) goto bad_width;
> +        vpl011_read_data(v->domain, &ch);
> +        *r = ch;
> +        break;
> +
> +    case RSR:
> +        if ( !VALID_BW_SIZE(dabt.size) ) goto bad_width;
> +
> +        /* It always returns 0 as there are no physical errors. */
> +        *r = 0;
> +        break;
> +
> +    case FR:
> +        if ( !VALID_BW_SIZE(dabt.size) ) goto bad_width;
> +        *r = (vpl011->uartfr & vpl011_reg_mask[dabt.size]);
> +        break;
> +
> +    case RIS:
> +        if ( !VALID_W_SIZE(dabt.size) ) goto bad_width;
> +        *r = (vpl011->uartris & vpl011_reg_mask[dabt.size]);
> +        break;
> +
> +    case MIS:
> +        if ( !VALID_W_SIZE(dabt.size) ) goto bad_width;
> +        *r = (vpl011->uartris &
> +                            vpl011->uartimsc & vpl011_reg_mask[dabt.size]);
> +        break;
> +
> +    case IMSC:
> +        if ( !VALID_W_SIZE(dabt.size) ) goto bad_width;
> +        *r = (vpl011->uartimsc & vpl011_reg_mask[dabt.size]);
> +        break;
> +
> +    case ICR:
> +        if ( !VALID_W_SIZE(dabt.size) ) 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)
> +{
> +    uint8_t ch = ((struct uartdr_reg *)&r)->data;
> +    struct hsr_dabt dabt = info->dabt;
> +    int vpl011_reg = (int)(info->gpa - GUEST_PL011_BASE);
> +    struct vpl011_s *vpl011 = &v->domain->arch.vpl011;
> +
> +    switch ( vpl011_reg )
> +    {
> +    case DR:
> +
> +        if ( !VALID_BW_SIZE(dabt.size) ) goto bad_width;
> +        vpl011_write_data(v->domain, ch);
> +        break;
> +
> +    case RSR: /* Nothing to clear. */
> +        if ( !VALID_BW_SIZE(dabt.size) ) goto bad_width;
> +        break;
> +
> +    case FR:
> +        goto write_ignore;
> +    case RIS:
> +    case MIS:
> +        goto word_write_ignore;
> +
> +    case IMSC:
> +        if ( !VALID_W_SIZE(dabt.size) ) goto bad_width;
> +        vpl011->uartimsc = (r & vpl011_reg_mask[dabt.size]);
> +        vgic_inject_vpl011_spi(v->domain);
> +        break;
> +
> +    case ICR:
> +        if ( !VALID_W_SIZE(dabt.size) ) goto bad_width;
> +        vpl011->uartris &= ~(r & vpl011_reg_mask[dabt.size]);
> +        vgic_inject_vpl011_spi(v->domain);
> +        break;
> +
> +    default:
> +        gprintk(XENLOG_ERR, "vpl011: unhandled write r%d offset %#08x\n",
> +                               dabt.reg, vpl011_reg);
> +        return 0;
> +    }
> +
> +    return 1;
> +
> +write_ignore:
> +    if ( !VALID_BW_SIZE(dabt.size) ) goto bad_width;
> +    return 1;
> +
> +word_write_ignore:
> +    if ( !VALID_W_SIZE(dabt.size) ) goto bad_width;
> +    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,
> +};
> +
> +int vpl011_map_guest_page(struct domain *d)
> +{
> +    struct vpl011_s *vpl011 = &d->arch.vpl011;
> +
> +    /* Map the guest PFN to Xen address space. */
> +    return prepare_ring_for_helper(d,
> +                                   
> d->arch.hvm_domain.params[HVM_PARAM_VCONSOLE_PFN],
> +                                   &vpl011->ring_page,
> +                                   &vpl011->ring_buf);
> +}
> +
> +static void vpl011_data_avail(struct domain *d)
> +{
> +    unsigned long flags;
> +    struct vpl011_s *vpl011 = &d->arch.vpl011;
> +    struct xencons_interface *intf=(struct xencons_interface 
> *)vpl011->ring_buf;
> +
> +    VPL011_LOCK(d, flags);
> +
> +    /* Update the uart rx state if the buffer is not empty. */
> +    if ( !VPL011_IN_RING_EMPTY(intf) )
> +    {
> +        vpl011->uartfr &= ~(RXFE);
> +        if ( VPL011_IN_RING_FULL(intf) )
> +            vpl011->uartfr |= (RXFF);
> +        vpl011->uartris |= (RXI);
> +    }
> +
> +    /* Update the uart tx state if the buffer is not full. */
> +    if ( !VPL011_OUT_RING_FULL(intf) )
> +    {
> +        vpl011->uartfr &= ~(TXFF);
> +        vpl011->uartris |= (TXI);
> +        if ( VPL011_OUT_RING_EMPTY(intf) )
> +        {
> +            vpl011->uartfr &= ~(BUSY);
> +            vpl011->uartfr |= (TXFE);

It is not a good idea to check the intf values twice: xenconsoled might
be modifying them, so we can get into the situation where intf->out*
change in between the two checks. Please read out_cons and out_prod only
once in this function.


> +        }
> +    }
> +
> +    VPL011_UNLOCK(d, flags);
> +
> +    vgic_inject_vpl011_spi(d);
> +
> +    if ( !VPL011_OUT_RING_EMPTY(intf) )
> +    {
> +        ASSERT( d->arch.hvm_domain.params[HVM_PARAM_VCONSOLE_EVTCHN] != 0 );
> +        notify_via_xen_event_channel(d, 
> d->arch.hvm_domain.params[HVM_PARAM_VCONSOLE_EVTCHN]);

Why are we sending notifications at this point? The out buffer hasn't
changed since xenconsoled sent the evtchn to Xen, so xenconsoled already
knows at this point that the out ring is not empty.


> +    }
> +}
> +
> +
> +static void vpl011_notification(struct vcpu *v, unsigned int port)
> +{
> +    vpl011_data_avail(v->domain);
> +}
> +
> +int domain_vpl011_init(struct domain *d, struct xen_arch_domainconfig 
> *config)
> +{
> +    int rc;
> +    struct vpl011_s *vpl011 = &d->arch.vpl011;
> +
> +    rc = alloc_unbound_xen_event_channel(d, 0, config->console_domid,
> +                                         vpl011_notification);
> +    if (rc < 0)
> +    {
> +        return rc;
> +    }
> +    d->arch.hvm_domain.params[HVM_PARAM_VCONSOLE_EVTCHN] = rc;
> +    rc = vgic_reserve_virq(d, GUEST_VPL011_SPI);
> +    if ( !rc )
> +        return rc;

We should free the allocated evtchn in case of error here


> +    register_mmio_handler(d, &vpl011_mmio_handler, GUEST_PL011_BASE, 
> GUEST_PL011_SIZE, NULL);
> +    spin_lock_init(&vpl011->lock);
> +
> +    vpl011->intialized = true;
> +
> +    return 0;
> +}
> +
> +int domain_vpl011_deinit(struct domain *d)
> +{
> +    struct vpl011_s *vpl011 = &d->arch.vpl011;
> +
> +    if ( vpl011->intialized )
> +    {
> +        free_xen_event_channel(d, 
> d->arch.hvm_domain.params[HVM_PARAM_VCONSOLE_EVTCHN]);
> +        destroy_ring_for_helper(&vpl011->ring_buf, vpl011->ring_page);
> +    }
> +
> +    return 0;
> +}
> +
> diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
> index 2d6fbb1..a122504 100644
> --- a/xen/include/asm-arm/domain.h
> +++ b/xen/include/asm-arm/domain.h
> @@ -11,6 +11,7 @@
>  #include <asm/gic.h>
>  #include <public/hvm/params.h>
>  #include <xen/serial.h>
> +#include <xen/vpl011.h>
>  
>  struct hvm_domain
>  {
> @@ -131,6 +132,10 @@ struct arch_domain
>      struct {
>          uint8_t privileged_call_enabled : 1;
>      } monitor;
> +
> +#ifdef CONFIG_VPL011_CONSOLE
> +    struct vpl011_s 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/public/arch-arm.h b/xen/include/public/arch-arm.h
> index bd974fb..5f91207 100644
> --- a/xen/include/public/arch-arm.h
> +++ b/xen/include/public/arch-arm.h
> @@ -322,6 +322,8 @@ struct xen_arch_domainconfig {
>       *
>       */
>      uint32_t clock_frequency;
> +
> +    uint32_t console_domid;
>  };
>  #endif /* __XEN__ || __XEN_TOOLS__ */
>  
> @@ -410,6 +412,10 @@ 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 +450,8 @@ 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/xen/vpl011.h b/xen/include/xen/vpl011.h
> new file mode 100644
> index 0000000..f9f2aba
> --- /dev/null
> +++ b/xen/include/xen/vpl011.h
> @@ -0,0 +1,67 @@
> +/*
> + * 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_
> +
> +/* helper macros */
> +#define VPL011_RING_DEPTH(intf,dir) (((intf)->dir ## _prod - (intf)->dir ## 
> _cons))
> +
> +#define VPL011_RING_MAX_DEPTH(intf,dir) (sizeof((intf)->dir)-1)
> +
> +#define VPL011_IN_RING_EMPTY(intf) (VPL011_RING_DEPTH(intf, in) == 0)
> +
> +#define VPL011_OUT_RING_EMPTY(intf) (VPL011_RING_DEPTH(intf, out) == 0)
> +
> +#define VPL011_IN_RING_FULL(intf) (VPL011_RING_DEPTH(intf, in) == 
> VPL011_RING_MAX_DEPTH(intf, in))
> +
> +#define VPL011_OUT_RING_FULL(intf) (VPL011_RING_DEPTH(intf, out) == 
> VPL011_RING_MAX_DEPTH(intf,out))
> +
> +#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)
> +
> +#define VALID_BW_SIZE(size) ( size == DABT_BYTE || size == DABT_HALF_WORD || 
> size == DABT_WORD )
> +#define VALID_W_SIZE(size)  ( size == DABT_HALF_WORD || size == DABT_WORD )
> +
> +struct uartdr_reg {
> +    uint8_t data;
> +    uint8_t error_status:4;
> +    uint8_t reserved1:4;
> +    uint16_t reserved2;
> +    uint32_t reserved3;
> +};
> +
> +struct vpl011_s {
> +    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;
> +    bool        intialized; /* flag which tells whether vpl011 is 
> initialized */
> +};
> +
> +int domain_vpl011_init(struct domain *d, struct xen_arch_domainconfig 
> *config);
> +int domain_vpl011_deinit(struct domain *d);
> +int vpl011_map_guest_page(struct domain *d);
> +
> +#endif
> -- 
> 2.7.4
> 

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