svn commit: r183836 - head/sys/arm/arm

[Rafal Jaworowski]

Author: raj
Date: Mon Oct 13 18:42:25 2008
New Revision: 183836
URL: http://svn.freebsd.org/changeset/base/183836

Log:
  Do not use cached page for temporary mapping in pmap_zero_page_generic()
  
  The physical page which we clear is accessed via additional temp kernel
  mapping for the period of zeroing operation. However in systems with virtual
  d-cache (most ARMs) when write-allocate feature is enabled, we can have
  modified but unflushed content pertaining to this physical page still in the
  d-cache due to its primary (pre-existing) mapping. In such scenario that
  cached content upon flush is likely to overwrite [portions of] the physical
  page we want to zero here..
  
  This is a general problem with multiple virtual mappings covering the same
  physical page with write-allocate and virtual d-cache: there is inherent
  potential for corruptions of this kind, which are not easily resolved; it is
  best policy that such multiple mappings be not allowed.
  
  Obtained from:	Marvell, Semihalf

Modified:
  head/sys/arm/arm/pmap.c

Modified: head/sys/arm/arm/pmap.c
==============================================================================
--- head/sys/arm/arm/pmap.c	Mon Oct 13 18:16:54 2008	(r183835)
+++ head/sys/arm/arm/pmap.c	Mon Oct 13 18:42:25 2008	(r183836)
@@ -3850,21 +3850,19 @@ pmap_zero_page_generic(vm_paddr_t phys, 
 
 	mtx_lock(&cmtx);
 	/*
-	 * Hook in the page, zero it, and purge the cache for that
-	 * zeroed page. Invalidate the TLB as needed.
+	 * Hook in the page, zero it, invalidate the TLB as needed.
+	 *
+	 * Note the temporary zero-page mapping must be a non-cached page in
+	 * ordert to work without corruption when write-allocate is enabled.
 	 */
-	*cdst_pte = L2_S_PROTO | phys |
-	    L2_S_PROT(PTE_KERNEL, VM_PROT_WRITE) | pte_l2_s_cache_mode;
-	PTE_SYNC(cdst_pte);
+	*cdst_pte = L2_S_PROTO | phys | L2_S_PROT(PTE_KERNEL, VM_PROT_WRITE);
 	cpu_tlb_flushD_SE(cdstp);
 	cpu_cpwait();
-	if (off || size != PAGE_SIZE) {
+	if (off || size != PAGE_SIZE)
 		bzero((void *)(cdstp + off), size);
-		cpu_dcache_wbinv_range(cdstp + off, size);
-	} else {
+	else
 		bzero_page(cdstp);
-		cpu_dcache_wbinv_range(cdstp, PAGE_SIZE);
-	}
+
 	mtx_unlock(&cmtx);
 #endif
 }