x86: don't use destroy_xen_mappings() for vunmap()

Its attempt to tear down intermediate page table levels may race with
map_pages_to_xen() establishing them, and now that
map_domain_page_global() is backed by vmap() this teardown is also
wasteful (as it's very likely to need the same address space populated
again within foreseeable time).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
master commit: 68caac7f6f4687241a24e804a9fca19aa26fe183
master date: 2013-07-17 10:21:33 +0200

diff --git a/xen/common/vmap.c b/xen/common/vmap.c
index c2d8a8ce701b6be29e7ae36c584fde22022d749f..5f92be4f20055100fdaff901256310d85ee62883 100644 (file)
--- a/xen/common/vmap.c
+++ b/xen/common/vmap.c
@@ -196,9 +196,13 @@ void *vmap(const unsigned long *mfn, unsigned int nr)
 
 void vunmap(const void *va)
 {
+#ifndef _PAGE_NONE
     unsigned long addr = (unsigned long)va;
 
     destroy_xen_mappings(addr, addr + PAGE_SIZE * vm_size(va));
+#else /* Avoid tearing down intermediate page tables. */
+    map_pages_to_xen((unsigned long)va, 0, vm_size(va), _PAGE_NONE);
+#endif
     vm_free(va);
 }
 #endif

diff --git a/xen/include/asm-x86/page.h b/xen/include/asm-x86/page.h
index 998a0c79dd787375a6c2a8b9c03940342f68ec86..2c3cc2dddfe556ce7704b7a8738a4a1840acefec 100644 (file)
--- a/xen/include/asm-x86/page.h
+++ b/xen/include/asm-x86/page.h
@@ -288,6 +288,7 @@ extern l1_pgentry_t l1_identmap[L1_PAGETABLE_ENTRIES],
 void paging_init(void);
 #endif /* !defined(__ASSEMBLY__) */
 
+#define _PAGE_NONE     _AC(0x000,U)
 #define _PAGE_PRESENT  _AC(0x001,U)
 #define _PAGE_RW       _AC(0x002,U)
 #define _PAGE_USER     _AC(0x004,U)