[xen master] Arm/P2M: reduce locking in p2m_{alloc,free}_page()

[patchbot@xxxxxxx]

commit 68f551ec5fa9ad96397a62cd463a7ff7e4db72d0
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Nov 29 15:39:57 2022 +0100
Commit:     Julien Grall <julien@xxxxxxx>
CommitDate: Sat Dec 3 18:12:11 2022 +0000

    Arm/P2M: reduce locking in p2m_{alloc,free}_page()
    
    It is generally preferable to not hold locks around allocation
    functions. And indeed in the hwdom case there's no point at all to hold
    the paging lock. Reduce the locked regions to the non-hwdom case, while
    at the same time arranging for p2m_alloc_page() to have just a single
    return point.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
---
 xen/arch/arm/p2m.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index fee830192a..08e5ac3def 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -48,7 +48,6 @@ static struct page_info *p2m_alloc_page(struct domain *d)
 {
     struct page_info *pg;
 
-    spin_lock(&d->arch.paging.lock);
     /*
      * For hardware domain, there should be no limit in the number of pages 
that
      * can be allocated, so that the kernel may take advantage of the extended
@@ -58,34 +57,28 @@ static struct page_info *p2m_alloc_page(struct domain *d)
     {
         pg = alloc_domheap_page(NULL, 0);
         if ( pg == NULL )
-        {
             printk(XENLOG_G_ERR "Failed to allocate P2M pages for hwdom.\n");
-            spin_unlock(&d->arch.paging.lock);
-            return NULL;
-        }
     }
     else
     {
+        spin_lock(&d->arch.paging.lock);
         pg = page_list_remove_head(&d->arch.paging.p2m_freelist);
-        if ( unlikely(!pg) )
-        {
-            spin_unlock(&d->arch.paging.lock);
-            return NULL;
-        }
+        spin_unlock(&d->arch.paging.lock);
     }
-    spin_unlock(&d->arch.paging.lock);
 
     return pg;
 }
 
 static void p2m_free_page(struct domain *d, struct page_info *pg)
 {
-    spin_lock(&d->arch.paging.lock);
     if ( is_hardware_domain(d) )
         free_domheap_page(pg);
     else
+    {
+        spin_lock(&d->arch.paging.lock);
         page_list_add_tail(pg, &d->arch.paging.p2m_freelist);
-    spin_unlock(&d->arch.paging.lock);
+        spin_unlock(&d->arch.paging.lock);
+    }
 }
 
 /* Return the size of the pool, in bytes. */
--
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