[PATCH v9] xen/console: introduce domain_console struct

[dmkhn@xxxxxxxxx]

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 allocation size to 256. No extra symbol for the
value since it is used only once during data structure declaration. All size
checks use ARRAY_SIZE().

Allocate domain_console from the heap so that the parent domain struct size
stays below PAGE_SIZE boundary to account for more console-related fields
added in the future. Ensure accesses to domain_console pointer are valid in
console_switch_input() and hvm_print_line().

Finally, update the domain_console allocation and initialization code.

No functional change.

Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
Changes since v8:
- ensure accesses to domain_console pointer are valid in
  console_switch_input() and hvm_print_line()
- updated comment for domain_console field

Link to v8: 
https://lore.kernel.org/xen-devel/20250716020447.1029992-1-dmukhin@xxxxxxxx/
---
 xen/arch/arm/vpl011.c      |  2 +-
 xen/arch/x86/hvm/hvm.c     | 22 ++++++++++++++--------
 xen/arch/x86/pv/shim.c     |  2 +-
 xen/common/domain.c        | 19 +++++++++----------
 xen/drivers/char/console.c | 28 ++++++++++++++++------------
 xen/include/xen/sched.h    | 24 +++++++++++++-----------
 6 files changed, 54 insertions(+), 43 deletions(-)

diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
index 480fc664fc62..d0d17c76b72c 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 56c7de39778b..394b07303a60 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;
+    struct domain *d = current->domain;
+    struct domain_console *cons = d->console;
     char c = *val;
 
     ASSERT(bytes == 1 && port == XEN_HVM_DEBUGCONS_IOPORT);
@@ -571,16 +572,21 @@ static int cf_check hvm_print_line(
     if ( !is_console_printable(c) )
         return X86EMUL_OKAY;
 
-    spin_lock(&cd->pbuf_lock);
+    rcu_lock_domain(d);
+
+    spin_lock(&cons->lock);
+    ASSERT(cons->idx < ARRAY_SIZE(cons->buf));
     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 == (ARRAY_SIZE(cons->buf) - 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);
+
+    rcu_unlock_domain(d);
 
     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 c5afac9f7259..7ed0523b7200 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -523,7 +523,7 @@ 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);
@@ -564,10 +564,13 @@ static void console_switch_input(void)
         d = rcu_lock_domain_by_id(domid);
         if ( d )
         {
-            rcu_unlock_domain(d);
-
-            if ( !d->console.input_allowed )
+            if ( !d->console->input_allowed )
+            {
+                rcu_unlock_domain(d);
                 continue;
+            }
+
+            rcu_unlock_domain(d);
 
             console_rx = next_rx;
             printk("*** Serial input to DOM%u", domid);
@@ -746,6 +749,7 @@ 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
@@ -758,22 +762,22 @@ 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) < (ARRAY_SIZE(cons->buf) - 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..c828d5626dea 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -371,6 +371,17 @@ struct evtchn_port_ops;
 
 #define MAX_NR_IOREQ_SERVERS 8
 
+/* 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. */
+    unsigned int idx;
+    spinlock_t lock;
+    char buf[256];
+};
+
 struct domain
 {
     domid_t          domain_id;
@@ -562,12 +573,6 @@ 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;
 
@@ -652,11 +657,8 @@ struct domain
     const unsigned int *llc_colors;
 #endif
 
-    /* Console settings. */
-    struct {
-        /* Permission to take ownership of the physical console input. */
-        bool input_allowed;
-    } console;
+    /* Pointer to console settings; NULL for system Xen domains. */
+    struct domain_console *console;
 } __aligned(PAGE_SIZE);
 
 static inline struct page_list_head *page_to_list(
-- 
2.34.1