Re: [PATCH v5] xen/console: introduce domain_console struct

[dmkhn@xxxxxxxxx]

On Wed, Jun 25, 2025 at 12:30:03AM +0000, dmkhn@xxxxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx> 
> 
> Introduce domain_console for grouping data structures used for integrating
> domain's diagnostic console with Xen's console driver.
> 
> Group all pbuf-related data structures under domain_console. Rename the moved
> fields to plain .buf, .idx and .lock names, since all uses of the fields are
> touched.
> 
> Bump the domain console buffer size to the closest power of 2 (256) and
> rename the symbol to DOMAIN_CONSOLE_BUF_SIZE.
> 
> Finally, update the domain_console allocation and initialization code.
> 
> No functional change.
> 
> Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>

Can I ask for review?

> ---
> Changes since v4:
> - use xvfree() in _domain_destroy()
> 
> Link to v4: https://lore.kernel.org/r/20250623202030.208655-1-dmukhin@xxxxxxxx
> CI: https://gitlab.com/xen-project/people/dmukhin/xen/-/pipelines/1887593859
> ---
>  xen/arch/arm/vpl011.c      |  2 +-
>  xen/arch/x86/hvm/hvm.c     | 17 +++++++++--------
>  xen/arch/x86/pv/shim.c     |  2 +-
>  xen/common/domain.c        | 19 +++++++++----------
>  xen/drivers/char/console.c | 21 +++++++++++----------
>  xen/include/xen/sched.h    | 30 ++++++++++++++++++++----------
>  6 files changed, 51 insertions(+), 40 deletions(-)
> 
> diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
> index 2b6f2a09bca6..f4a840da10c5 100644
> --- a/xen/arch/arm/vpl011.c
> +++ b/xen/arch/arm/vpl011.c
> @@ -713,7 +713,7 @@ int domain_vpl011_init(struct domain *d, struct 
> vpl011_init_info *info)
>      }
>      else
>      {
> -        d->console.input_allowed = true;
> +        d->console->input_allowed = true;
>          vpl011->backend_in_domain = false;
>  
>          vpl011->backend.xen = xzalloc(struct vpl011_xen_backend);
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 056360d5fe50..7d599eab73f2 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -559,7 +559,8 @@ void hvm_do_resume(struct vcpu *v)
>  static int cf_check hvm_print_line(
>      int dir, unsigned int port, unsigned int bytes, uint32_t *val)
>  {
> -    struct domain *cd = current->domain;
> +    const struct domain *d = current->domain;
> +    struct domain_console *cons = d->console;
>      char c = *val;
>  
>      ASSERT(bytes == 1 && port == XEN_HVM_DEBUGCONS_IOPORT);
> @@ -571,16 +572,16 @@ static int cf_check hvm_print_line(
>      if ( !is_console_printable(c) )
>          return X86EMUL_OKAY;
>  
> -    spin_lock(&cd->pbuf_lock);
> +    spin_lock(&cons->lock);
>      if ( c != '\n' )
> -        cd->pbuf[cd->pbuf_idx++] = c;
> -    if ( (cd->pbuf_idx == (DOMAIN_PBUF_SIZE - 1)) || (c == '\n') )
> +        cons->buf[cons->idx++] = c;
> +    if ( (cons->idx == (DOMAIN_CONSOLE_BUF_SIZE - 1)) || (c == '\n') )
>      {
> -        cd->pbuf[cd->pbuf_idx] = '\0';
> -        guest_printk(cd, XENLOG_G_DEBUG "%s\n", cd->pbuf);
> -        cd->pbuf_idx = 0;
> +        cons->buf[cons->idx] = '\0';
> +        guest_printk(d, XENLOG_G_DEBUG "%s\n", cons->buf);
> +        cons->idx = 0;
>      }
> -    spin_unlock(&cd->pbuf_lock);
> +    spin_unlock(&cons->lock);
>  
>      return X86EMUL_OKAY;
>  }
> diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c
> index bc2a7dd5fae5..bd29c53a2d34 100644
> --- a/xen/arch/x86/pv/shim.c
> +++ b/xen/arch/x86/pv/shim.c
> @@ -239,7 +239,7 @@ void __init pv_shim_setup_dom(struct domain *d, 
> l4_pgentry_t *l4start,
>       */
>      d->max_pages = domain_tot_pages(d);
>  
> -    d->console.input_allowed = true;
> +    d->console->input_allowed = true;
>  }
>  
>  static void write_start_info(struct domain *d)
> diff --git a/xen/common/domain.c b/xen/common/domain.c
> index 303c338ef293..caef4cc8d649 100644
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -669,7 +669,7 @@ static void _domain_destroy(struct domain *d)
>      BUG_ON(!d->is_dying);
>      BUG_ON(atomic_read(&d->refcnt) != DOMAIN_DESTROYED);
>  
> -    xfree(d->pbuf);
> +    xvfree(d->console);
>  
>      argo_destroy(d);
>  
> @@ -835,8 +835,6 @@ struct domain *domain_create(domid_t domid,
>          flags |= CDF_hardware;
>          if ( old_hwdom )
>              old_hwdom->cdf &= ~CDF_hardware;
> -
> -        d->console.input_allowed = true;
>      }
>  
>      /* Holding CDF_* internal flags. */
> @@ -866,8 +864,6 @@ struct domain *domain_create(domid_t domid,
>      spin_lock_init(&d->shutdown_lock);
>      d->shutdown_code = SHUTDOWN_CODE_INVALID;
>  
> -    spin_lock_init(&d->pbuf_lock);
> -
>      rwlock_init(&d->vnuma_rwlock);
>  
>  #ifdef CONFIG_HAS_PCI
> @@ -877,6 +873,14 @@ struct domain *domain_create(domid_t domid,
>  
>      /* All error paths can depend on the above setup. */
>  
> +    err = -ENOMEM;
> +    d->console = xvzalloc(typeof(*d->console));
> +    if ( !d->console )
> +        goto fail;
> +
> +    spin_lock_init(&d->console->lock);
> +    d->console->input_allowed = is_hardware_domain(d);
> +
>      /*
>       * Allocate d->vcpu[] and set ->max_vcpus up early.  Various per-domain
>       * resources want to be sized based on max_vcpus.
> @@ -959,11 +963,6 @@ struct domain *domain_create(domid_t domid,
>      if ( (err = argo_init(d)) != 0 )
>          goto fail;
>  
> -    err = -ENOMEM;
> -    d->pbuf = xzalloc_array(char, DOMAIN_PBUF_SIZE);
> -    if ( !d->pbuf )
> -        goto fail;
> -
>      if ( (err = sched_init_domain(d, config->cpupool_id)) != 0 )
>          goto fail;
>  
> diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> index 5d3681b16aee..a894dc6dc3b2 100644
> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -524,7 +524,7 @@ struct domain *console_get_domain(void)
>      if ( !d )
>          return NULL;
>  
> -    if ( d->console.input_allowed )
> +    if ( d->console->input_allowed )
>          return d;
>  
>      rcu_unlock_domain(d);
> @@ -567,7 +567,7 @@ static void console_switch_input(void)
>          {
>              rcu_unlock_domain(d);
>  
> -            if ( !d->console.input_allowed )
> +            if ( !d->console->input_allowed )
>                  continue;
>  
>              console_rx = next_rx;
> @@ -757,6 +757,7 @@ static long 
> guest_console_write(XEN_GUEST_HANDLE_PARAM(char) buffer,
>          else
>          {
>              char *kin = kbuf, *kout = kbuf, c;
> +            struct domain_console *cons = cd->console;
>  
>              /* Strip non-printable characters */
>              do
> @@ -769,22 +770,22 @@ static long 
> guest_console_write(XEN_GUEST_HANDLE_PARAM(char) buffer,
>              } while ( --kcount > 0 );
>  
>              *kout = '\0';
> -            spin_lock(&cd->pbuf_lock);
> +            spin_lock(&cons->lock);
>              kcount = kin - kbuf;
>              if ( c != '\n' &&
> -                 (cd->pbuf_idx + (kout - kbuf) < (DOMAIN_PBUF_SIZE - 1)) )
> +                 (cons->idx + (kout - kbuf) < (DOMAIN_CONSOLE_BUF_SIZE - 1)) 
> )
>              {
>                  /* buffer the output until a newline */
> -                memcpy(cd->pbuf + cd->pbuf_idx, kbuf, kout - kbuf);
> -                cd->pbuf_idx += (kout - kbuf);
> +                memcpy(cons->buf + cons->idx, kbuf, kout - kbuf);
> +                cons->idx += kout - kbuf;
>              }
>              else
>              {
> -                cd->pbuf[cd->pbuf_idx] = '\0';
> -                guest_printk(cd, XENLOG_G_DEBUG "%s%s\n", cd->pbuf, kbuf);
> -                cd->pbuf_idx = 0;
> +                cons->buf[cons->idx] = '\0';
> +                guest_printk(cd, XENLOG_G_DEBUG "%s%s\n", cons->buf, kbuf);
> +                cons->idx = 0;
>              }
> -            spin_unlock(&cd->pbuf_lock);
> +            spin_unlock(&cons->lock);
>          }
>  
>          guest_handle_add_offset(buffer, kcount);
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index fe53d4fab7ba..3c74dc71fe5e 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -371,6 +371,25 @@ struct evtchn_port_ops;
>  
>  #define MAX_NR_IOREQ_SERVERS 8
>  
> +/*
> + * Arbitrary value.
> + * The buffer is part of the dynamically-allocated data structure, using an
> + * even multiple of a cache line size may help to optimize the allocation
> + * overhead.
> + */
> +#define DOMAIN_CONSOLE_BUF_SIZE 256
> +
> +/* Domain console settings. */
> +struct domain_console {
> +    /* Permission to take ownership of the physical console input. */
> +    bool input_allowed;
> +
> +    /* hvm_print_line() and guest_console_write() logging. */
> +    spinlock_t lock;
> +    unsigned int idx;
> +    char buf[DOMAIN_CONSOLE_BUF_SIZE];
> +};
> +
>  struct domain
>  {
>      domid_t          domain_id;
> @@ -562,12 +581,6 @@ struct domain
>      /* Control-plane tools handle for this domain. */
>      xen_domain_handle_t handle;
>  
> -    /* hvm_print_line() and guest_console_write() logging. */
> -#define DOMAIN_PBUF_SIZE 200
> -    char       *pbuf;
> -    unsigned int pbuf_idx;
> -    spinlock_t  pbuf_lock;
> -
>      /* OProfile support. */
>      struct xenoprof *xenoprof;
>  
> @@ -653,10 +666,7 @@ struct domain
>  #endif
>  
>      /* Console settings. */
> -    struct {
> -        /* Permission to take ownership of the physical console input. */
> -        bool input_allowed;
> -    } console;
> +    struct domain_console *console;
>  } __aligned(PAGE_SIZE);
>  
>  static inline struct page_list_head *page_to_list(
> -- 
> 2.34.1
>