From: Julien Grall <julien.grall@arm.com>
Date: Mon, 16 Jul 2018 17:27:01 +0000 (+0100)
Subject: xen/arm: p2m: Reduce the locking section in get_page_from_gva
X-Git-Tag: archive/raspbian/4.14.0+80-gd101b417b7-1+rpi1^2~63^2~3415
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=0f11f3e7abf6465a8da8790af3f00518a74890fc;p=xen.git

xen/arm: p2m: Reduce the locking section in get_page_from_gva

The p2m lock is only necessary to prevent gvirt_to_maddr failing when
break-before-make sequence is used in the P2M update concurrently on
another pCPU. So reduce the locking section.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
---

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 14791388ad..5ca7ffe41b 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1415,9 +1415,13 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
     if ( v != current )
         return NULL;
 
+    /*
+     * The lock is here to protect us against the break-before-make
+     * sequence used when updating the entry.
+     */
     p2m_read_lock(p2m);
-
     par = gvirt_to_maddr(va, &maddr, flags);
+    p2m_read_unlock(p2m);
 
     if ( par )
     {
@@ -1445,8 +1449,6 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
     }
 
 err:
-    p2m_read_unlock(p2m);
-
     if ( !page && p2m->mem_access_enabled )
         page = p2m_mem_access_check_and_get_page(va, flags, v);