[PATCH v6 4/4] xen/console: switch conring runtime allocation to xvmalloc

[dmukhin@xxxxxxxx]

From: Denis Mukhin <dmukhin@xxxxxxxx> 

The console ring only needs to be virtually contiguous; it does not need
a naturally aligned or physically contiguous allocation. Replace the
runtime xenheap allocation in console_init_ring() with an xvmalloc-backed
buffer.

Also clamp the user-configured ring size to the supported range and emit
warnings when the requested size is adjusted.

Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
Changes since v5:
- switched to xvmalloc_array()
- fixed conring size checks
- corrected diagnostic messages
---
 xen/drivers/char/console.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 5cac87d052b9..29b9359468e7 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -33,6 +33,7 @@
 #include <asm/setup.h>
 #include <xen/sections.h>
 #include <xen/consoled.h>
+#include <xen/xvmalloc.h>
 
 #ifdef CONFIG_X86
 #include <asm/guest.h>
@@ -343,6 +344,7 @@ static void cf_check do_dec_thresh(unsigned char key, bool 
unused)
 static unsigned int __initdata opt_conring_size;
 size_param("conring_size", opt_conring_size);
 
+#define CONRING_SIZE_MIN    (1U << 14)
 #define _CONRING_SIZE       (1U << CONFIG_CONRING_SHIFT)
 #define CONRING_IDX_MASK(i) ((i) & (conring_size - 1))
 static char __initdata _conring[_CONRING_SIZE];
@@ -464,20 +466,33 @@ void __init console_init_ring(void)
 {
     char *ring;
     XENCONS_RING_IDX i, size;
-    unsigned int order, memflags;
+    unsigned int order;
     unsigned long flags;
 
     if ( !opt_conring_size )
         return;
 
     order = get_order_from_bytes(max(opt_conring_size, conring_size));
-    memflags = MEMF_bits(crashinfo_maxaddr_bits);
-    while ( (ring = alloc_xenheap_pages(order, memflags)) == NULL )
+    size = PAGE_SIZE << order;
+    if ( size != opt_conring_size )
     {
-        BUG_ON(order == 0);
-        order--;
+        opt_conring_size = size;
+        printk(XENLOG_WARNING "Normalizing console ring size.\n");
     }
-    opt_conring_size = PAGE_SIZE << order;
+    if ( opt_conring_size < CONRING_SIZE_MIN )
+    {
+        opt_conring_size = 0;
+        printk(XENLOG_WARNING "Ignoring too-small console ring size 
override.\n");
+        return;
+    }
+    else if ( opt_conring_size > GB(2) )
+    {
+        opt_conring_size = GB(2);
+        printk(XENLOG_WARNING "Limiting user-configured console ring size to 2 
GiB.\n");
+    }
+
+    ring = xvmalloc_array(char, opt_conring_size);
+    BUG_ON(ring == NULL);
 
     nrspin_lock_irqsave(&console_lock, flags);
 
-- 
2.54.0