From: Denis Mukhin <dmukhin@ford.com>

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@ford.com>
---
Changes since v2:
- fixed domain_console definition
- dropped changes under CONFIG_VERBOSE_DEBUG
- fixed domain_console allocation/initilization in domain_create()
- switched hvm_print_line() to use `d` for domain pointer

Link to v2: https://lore.kernel.org/r/20250617012713.57074-1-dmukhin@ford.com
---
 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 | 22 ++++++++++++----------
 xen/include/xen/sched.h    | 25 +++++++++++++++----------
 6 files changed, 47 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 434d32901b1b..2f6b0af50dd3 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);
+    xfree(d->console);
 
     argo_destroy(d);
 
@@ -832,8 +832,6 @@ 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. */
@@ -863,8 +861,6 @@ 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
@@ -874,6 +870,14 @@ 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.
@@ -956,11 +960,6 @@ 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..5188ee761dd2 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 +770,23 @@ 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..252f0e8c4aa8 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -371,6 +371,20 @@ struct evtchn_port_ops;
 
 #define MAX_NR_IOREQ_SERVERS 8
 
+/* Arbitrary value. */
+#define DOMAIN_CONSOLE_BUF_SIZE 256
+
+/* Domain console settings. */
+struct domain_console {
+    /* hvm_print_line() and guest_console_write() logging. */
+    char buf[DOMAIN_CONSOLE_BUF_SIZE];
+    unsigned int idx;
+    spinlock_t lock;
+
+    /* Permission to take ownership of the physical console input. */
+    bool input_allowed;
+};
+
 struct domain
 {
     domid_t          domain_id;
@@ -562,12 +576,6 @@ 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 +661,7 @@ 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

On 23.06.2025 03:34, dmkhn@proton.me wrote:
> @@ -769,22 +770,23 @@ 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 )

The dropping of the parentheses around the pointer subtraction is
problematic: You open up UB opportunities this way, as evaluation order
changes. We had UBSAN trip up on similar constructs already in the past.

>              {
>                  /* 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);

Here, otoh, the parentheses could be dropped while touching the line.

>              }
>              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);

There's no need to wrap lines here, is there?

> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -371,6 +371,20 @@ struct evtchn_port_ops;
>  
>  #define MAX_NR_IOREQ_SERVERS 8
>  
> +/* Arbitrary value. */
> +#define DOMAIN_CONSOLE_BUF_SIZE 256

Nit: The value isn't entirely arbitrary.

> +/* Domain console settings. */
> +struct domain_console {
> +    /* hvm_print_line() and guest_console_write() logging. */
> +    char buf[DOMAIN_CONSOLE_BUF_SIZE];

This placement will negatively affect code generation on at least x86.
I did suggest putting the array at the end, for this very reason.

Jan