svn commit: r269238 - stable/10/sys/amd64/amd64

[Marius Strobl]

Author: marius
Date: Tue Jul 29 13:11:37 2014
New Revision: 269238
URL: http://svnweb.freebsd.org/changeset/base/269238

Log:
  MFC: r269051
  
  Copying pages via temporary mappings in the !DMAP case of pmap_copy_pages()
  involves updating the corresponding page tables followed by accesses to the
  pages in question. This sequence is subject to the situation exactly described
  in the "AMD64 Architecture Programmer's Manual Volume 2: System Programming"
  rev. 3.23, "7.3.1 Special Coherency Considerations" [1, p. 171 f.]. Therefore,
  issuing the INVLPG right after modifying the PTE bits is crucial (see also
  r269050, MFCed to stable/10 in r269235).
  For the amd64 PMAP code, the order of instructions was already correct. The
  above fact still is worth documenting, though.
  
  1: http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2012/10/24593_APM_v21.pdf
  
  Reviewed by:	alc
  Sponsored by:	Bally Wulff Games & Entertainment GmbH

Modified:
  stable/10/sys/amd64/amd64/pmap.c
Directory Properties:
  stable/10/   (props changed)

Modified: stable/10/sys/amd64/amd64/pmap.c
==============================================================================
--- stable/10/sys/amd64/amd64/pmap.c	Tue Jul 29 13:08:56 2014	(r269237)
+++ stable/10/sys/amd64/amd64/pmap.c	Tue Jul 29 13:11:37 2014	(r269238)
@@ -4984,6 +4984,14 @@ pmap_copy_pages(vm_page_t ma[], vm_offse
 	int cnt;
 	boolean_t pinned;
 
+	/*
+	 * NB:  The sequence of updating a page table followed by accesses
+	 * to the corresponding pages used in the !DMAP case is subject to
+	 * the situation described in the "AMD64 Architecture Programmer's
+	 * Manual Volume 2: System Programming" rev. 3.23, "7.3.1 Special
+	 * Coherency Considerations".  Therefore, issuing the INVLPG right
+	 * after modifying the PTE bits is crucial.
+	 */
 	pinned = FALSE;
 	while (xfersize > 0) {
 		a_pg_offset = a_offset & PAGE_MASK;