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Re: [Xen-devel] [PATCH v5 22/25] xen/arm: Allow vpl011 to be used by DomU



On Wed, 24 Oct 2018, Oleksandr Tyshchenko wrote:
> Hi, Stefano
> 
> On Tue, Oct 23, 2018 at 5:04 AM Stefano Stabellini
> <sstabellini@xxxxxxxxxx> wrote:
> >
> > Make vpl011 being able to be used without a userspace component in Dom0.
> > In that case, output is printed to the Xen serial and input is received
> > from the Xen serial one character at a time.
> >
> > Call domain_vpl011_init during construct_domU if vpl011 is enabled.
> >
> > Introduce a new ring struct with only the ring array to avoid a waste of
> > memory. Introduce separate read_data and write_data functions for
> > initial domains: vpl011_write_data_xen is very simple and just writes
> > to the console, while vpl011_read_data_xen is a duplicate of
> > vpl011_read_data. Although textually almost identical, we are forced to
> > duplicate the functions because the struct layout is different.
> >
> > Output characters are printed one by one, potentially leading to
> > intermixed output of different domains on the console. A follow-up patch
> > will solve the issue by introducing buffering.
> >
> > Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> > Acked-by: Julien Grall <julien.grall@xxxxxxx>
> > ---
> > Changes in v5:
> > - renable call to vpl011_rx_char_xen from console.c
> >
> > Changes in v4:
> > - code style
> >
> > Changes in v3:
> > - add in-code comments
> > - improve existing comments
> > - remove ifdef around domain_vpl011_init in construct_domU
> > - add ASSERT
> > - use SBSA_UART_FIFO_SIZE for in buffer size
> > - rename ring_enable to backend_in_domain
> > - rename struct xencons_in to struct vpl011_xen_backend
> > - rename inring field to xen
> > - rename helper functions accordingly
> > - remove unnecessary stub implementation of vpl011_rx_char
> > - move vpl011_rx_char_xen within the file to avoid the need of a forward
> >   declaration of vpl011_data_avail
> > - fix small bug in vpl011_rx_char_xen: increment in_prod before using it
> >   to check xencons_queued.
> >
> > Changes in v2:
> > - only init if vpl011
> > - rename vpl011_read_char to vpl011_rx_char
> > - remove spurious change
> > - fix coding style
> > - use different ring struct
> > - move the write_data changes to their own function
> >   (vpl011_write_data_noring)
> > - duplicate vpl011_read_data
> > ---
> >  xen/arch/arm/domain_build.c  |   9 +-
> >  xen/arch/arm/vpl011.c        | 200 
> > +++++++++++++++++++++++++++++++++++++------
> >  xen/drivers/char/console.c   |   2 +-
> >  xen/include/asm-arm/vpl011.h |   8 ++
> >  4 files changed, 193 insertions(+), 26 deletions(-)
> >
> > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > index 6026b77..9ffd919 100644
> > --- a/xen/arch/arm/domain_build.c
> > +++ b/xen/arch/arm/domain_build.c
> > @@ -2629,7 +2629,14 @@ static int __init construct_domU(struct domain *d,
> >      if ( rc < 0 )
> >          return rc;
> >
> > -    return construct_domain(d, &kinfo);
> > +    rc = construct_domain(d, &kinfo);
> > +    if ( rc < 0 )
> > +        return rc;
> > +
> > +    if ( kinfo.vpl011 )
> > +        rc = domain_vpl011_init(d, NULL);
> > +
> > +    return rc;
> >  }
> >
> >  void __init create_domUs(void)
> > diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
> > index 68452a8..131507e 100644
> > --- a/xen/arch/arm/vpl011.c
> > +++ b/xen/arch/arm/vpl011.c
> > @@ -77,6 +77,91 @@ static void vpl011_update_interrupt_status(struct domain 
> > *d)
> >  #endif
> >  }
> >
> > +/*
> > + * vpl011_write_data_xen writes chars from the vpl011 out buffer to the
> > + * console. Only to be used when the backend is Xen.
> > + */
> > +static void vpl011_write_data_xen(struct domain *d, uint8_t data)
> > +{
> > +    unsigned long flags;
> > +    struct vpl011 *vpl011 = &d->arch.vpl011;
> > +
> > +    VPL011_LOCK(d, flags);
> > +
> > +    printk("%c", data);
> > +    if (data == '\n')
> > +        printk("DOM%u: ", d->domain_id);
> > +
> > +    vpl011->uartris |= TXI;
> > +    vpl011->uartfr &= ~TXFE;
> > +    vpl011_update_interrupt_status(d);
> > +
> > +    VPL011_UNLOCK(d, flags);
> > +}
> > +
> > +/*
> > + * vpl011_read_data_xen reads data when the backend is xen. Characters
> > + * are added to the vpl011 receive buffer by vpl011_rx_char_xen.
> > + */
> > +static uint8_t vpl011_read_data_xen(struct domain *d)
> > +{
> > +    unsigned long flags;
> > +    uint8_t data = 0;
> > +    struct vpl011 *vpl011 = &d->arch.vpl011;
> > +    struct vpl011_xen_backend *intf = vpl011->backend.xen;
> > +    XENCONS_RING_IDX in_cons, in_prod;
> > +
> > +    VPL011_LOCK(d, flags);
> > +
> > +    in_cons = intf->in_cons;
> > +    in_prod = intf->in_prod;
> > +
> > +    smp_rmb();
> > +
> > +    /*
> > +     * 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 )
> > +    {
> > +        unsigned int fifo_level;
> > +
> > +        data = intf->in[xencons_mask(in_cons, sizeof(intf->in))];
> > +        in_cons += 1;
> > +        smp_mb();
> > +        intf->in_cons = in_cons;
> > +
> > +        fifo_level = xencons_queued(in_prod, in_cons, sizeof(intf->in));
> > +
> > +        /* If the FIFO is now empty, we clear the receive timeout 
> > interrupt. */
> > +        if ( fifo_level == 0 )
> > +        {
> > +            vpl011->uartfr |= RXFE;
> > +            vpl011->uartris &= ~RTI;
> > +        }
> > +
> > +        /* If the FIFO is more than half empty, we clear the RX interrupt. 
> > */
> > +        if ( fifo_level < sizeof(intf->in) - SBSA_UART_FIFO_LEVEL )
> > +            vpl011->uartris &= ~RXI;
> > +
> > +        vpl011_update_interrupt_status(d);
> > +    }
> > +    else
> > +        gprintk(XENLOG_ERR, "vpl011: Unexpected IN ring buffer empty\n");
> > +
> > +    /*
> > +     * We have consumed a character or the FIFO was empty, so clear the
> > +     * "FIFO full" bit.
> > +     */
> > +    vpl011->uartfr &= ~RXFF;
> > +
> > +    VPL011_UNLOCK(d, flags);
> > +
> > +    return data;
> > +}
> > +
> >  static uint8_t vpl011_read_data(struct domain *d)
> >  {
> >      unsigned long flags;
> > @@ -240,7 +325,10 @@ static int vpl011_mmio_read(struct vcpu *v,
> >      case DR:
> >          if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
> >
> > -        *r = vreg_reg32_extract(vpl011_read_data(d), info);
> > +        if ( vpl011->backend_in_domain )
> > +            *r = vreg_reg32_extract(vpl011_read_data(d), info);
> > +        else
> > +            *r = vreg_reg32_extract(vpl011_read_data_xen(d), info);
> >          return 1;
> >
> >      case RSR:
> > @@ -325,7 +413,10 @@ static int vpl011_mmio_write(struct vcpu *v,
> >
> >          vreg_reg32_update(&data, r, info);
> >          data &= 0xFF;
> > -        vpl011_write_data(v->domain, data);
> > +        if ( vpl011->backend_in_domain )
> > +            vpl011_write_data(v->domain, data);
> > +        else
> > +            vpl011_write_data_xen(v->domain, data);
> >          return 1;
> >      }
> >
> > @@ -430,6 +521,39 @@ static void vpl011_data_avail(struct domain *d,
> >          vpl011->uartfr |= TXFE;
> >  }
> >
> > +/*
> > + * vpl011_rx_char_xen adds a char to a domain's vpl011 receive buffer.
> > + * It is only used when the vpl011 backend is in Xen.
> > + */
> > +void vpl011_rx_char_xen(struct domain *d, char c)
> > +{
> > +    unsigned long flags;
> > +    struct vpl011 *vpl011 = &d->arch.vpl011;
> > +    struct vpl011_xen_backend *intf = vpl011->backend.xen;
> > +    XENCONS_RING_IDX in_cons, in_prod, in_fifo_level;
> > +
> > +    ASSERT(!vpl011->backend_in_domain);
> > +    VPL011_LOCK(d, flags);
> > +
> > +    in_cons = intf->in_cons;
> > +    in_prod = intf->in_prod;
> Do we need barriers here and after writing the ring?

We do not need barriers because both frontend and backend are in Xen for
this use-case: both in_cons and in_prod are modified by Xen with the
VPL011_LOCK held. There are no simultaneous reads/writes and the lock
includes a barrier.

 
> > +    if ( xencons_queued(in_prod, in_cons, sizeof(intf->in)) == 
> > sizeof(intf->in) )
> > +    {
> > +        VPL011_UNLOCK(d, flags);
> > +        return;
> > +    }
> > +
> > +    intf->in[xencons_mask(in_prod, sizeof(intf->in))] = c;
> > +    intf->in_prod = ++in_prod;
> > +
> > +    in_fifo_level = xencons_queued(in_prod,
> > +                                   in_cons,
> > +                                   sizeof(intf->in));
> > +
> > +    vpl011_data_avail(d, in_fifo_level, sizeof(intf->in), 0, 
> > SBSA_UART_FIFO_SIZE);
> > +    VPL011_UNLOCK(d, flags);
> > +}
> > +
> >  static void vpl011_notification(struct vcpu *v, unsigned int port)
> >  {
> >      unsigned long flags;
> > @@ -470,27 +594,47 @@ int domain_vpl011_init(struct domain *d, struct 
> > vpl011_init_info *info)
> >      if ( vpl011->backend.dom.ring_buf )
> >          return -EINVAL;
> >
> > -    /* Map the guest PFN to Xen address space. */
> > -    rc =  prepare_ring_for_helper(d,
> > -                                  gfn_x(info->gfn),
> > -                                  &vpl011->backend.dom.ring_page,
> > -                                  &vpl011->backend.dom.ring_buf);
> > -    if ( rc < 0 )
> > -        goto out;
> > +    /*
> > +     * info is NULL when the backend is in Xen.
> > +     * info is != NULL when the backend is in a domain.
> > +     */
> > +    if ( info != NULL )
> > +    {
> > +        vpl011->backend_in_domain = true;
> > +
> > +        /* Map the guest PFN to Xen address space. */
> > +        rc =  prepare_ring_for_helper(d,
> > +                                      gfn_x(info->gfn),
> > +                                      &vpl011->backend.dom.ring_page,
> > +                                      &vpl011->backend.dom.ring_buf);
> > +        if ( rc < 0 )
> > +            goto out;
> > +
> > +        rc = alloc_unbound_xen_event_channel(d, 0, info->console_domid,
> > +                                             vpl011_notification);
> > +        if ( rc < 0 )
> > +            goto out1;
> > +
> > +        vpl011->evtchn = info->evtchn = rc;
> > +    }
> > +    else
> > +    {
> > +        vpl011->backend_in_domain = false;
> > +
> > +        vpl011->backend.xen = xzalloc(struct vpl011_xen_backend);
> > +        if ( vpl011->backend.xen == NULL )
> > +        {
> > +            rc = -EINVAL;
> > +            goto out1;
> > +        }
> > +    }
> >
> >      rc = vgic_reserve_virq(d, GUEST_VPL011_SPI);
> >      if ( !rc )
> >      {
> >          rc = -EINVAL;
> > -        goto out1;
> > -    }
> > -
> > -    rc = alloc_unbound_xen_event_channel(d, 0, info->console_domid,
> > -                                         vpl011_notification);
> > -    if ( rc < 0 )
> >          goto out2;
> > -
> > -    vpl011->evtchn = info->evtchn = rc;
> > +    }
> >
> >      spin_lock_init(&vpl011->lock);
> >
> > @@ -503,8 +647,11 @@ out2:
> >      vgic_free_virq(d, GUEST_VPL011_SPI);
> >
> >  out1:
> > -    destroy_ring_for_helper(&vpl011->backend.dom.ring_buf,
> > -                                       vpl011->backend.dom.ring_page);
> > +    if ( vpl011->backend_in_domain )
> > +        destroy_ring_for_helper(&vpl011->backend.dom.ring_buf,
> > +                                vpl011->backend.dom.ring_page);
> > +    else
> > +        xfree(vpl011->backend.xen);
> >
> >  out:
> >      return rc;
> > @@ -514,12 +661,17 @@ void domain_vpl011_deinit(struct domain *d)
> >  {
> >      struct vpl011 *vpl011 = &d->arch.vpl011;
> >
> > -    if ( !vpl011->backend.dom.ring_buf )
> > -        return;
> > +    if ( vpl011->backend_in_domain )
> > +    {
> > +        if ( !vpl011->backend.dom.ring_buf )
> > +            return;
> >
> > -    free_xen_event_channel(d, vpl011->evtchn);
> > -    destroy_ring_for_helper(&vpl011->backend.dom.ring_buf,
> > -                                       vpl011->backend.dom.ring_page);
> > +        free_xen_event_channel(d, vpl011->evtchn);
> > +        destroy_ring_for_helper(&vpl011->backend.dom.ring_buf,
> > +                                vpl011->backend.dom.ring_page);
> > +    }
> > +    else
> > +        xfree(vpl011->backend.xen);
> >  }
> >
> >  /*
> > diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> > index 75172e7..990c51c 100644
> > --- a/xen/drivers/char/console.c
> > +++ b/xen/drivers/char/console.c
> > @@ -444,7 +444,7 @@ static void __serial_rx(char c, struct cpu_user_regs 
> > *regs)
> >          send_global_virq(VIRQ_CONSOLE);
> >          break;
> >      }
> > -#if 0
> > +#ifdef CONFIG_SBSA_VUART_CONSOLE
> >      default:
> >      {
> >          struct domain *d = rcu_lock_domain_by_any_id(console_rx - 1);
> > diff --git a/xen/include/asm-arm/vpl011.h b/xen/include/asm-arm/vpl011.h
> > index 42d7a24..5eb6d25 100644
> > --- a/xen/include/asm-arm/vpl011.h
> > +++ b/xen/include/asm-arm/vpl011.h
> > @@ -21,6 +21,7 @@
> >
> >  #include <public/domctl.h>
> >  #include <public/io/ring.h>
> > +#include <public/io/console.h>
> >  #include <asm/vreg.h>
> >  #include <xen/mm.h>
> >
> > @@ -29,13 +30,19 @@
> >  #define VPL011_UNLOCK(d,flags) 
> > spin_unlock_irqrestore(&(d)->arch.vpl011.lock, flags)
> >
> >  #define SBSA_UART_FIFO_SIZE 32
> > +struct vpl011_xen_backend {
> > +    char in[SBSA_UART_FIFO_SIZE];
> > +    XENCONS_RING_IDX in_cons, in_prod;
> > +};
> >
> >  struct vpl011 {
> > +    bool backend_in_domain;
> >      union {
> >          struct {
> >              void *ring_buf;
> >              struct page_info *ring_page;
> >          } dom;
> > +        struct vpl011_xen_backend *xen;
> >      } backend;
> >      uint32_t    uartfr;         /* Flag register */
> >      uint32_t    uartcr;         /* Control register */
> > @@ -57,6 +64,7 @@ struct vpl011_init_info {
> >  int domain_vpl011_init(struct domain *d,
> >                         struct vpl011_init_info *info);
> >  void domain_vpl011_deinit(struct domain *d);
> > +void vpl011_rx_char_xen(struct domain *d, char c);
> >  #else
> >  static inline int domain_vpl011_init(struct domain *d,
> >                                       struct vpl011_init_info *info)

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