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[PATCH] remap_file_pages needs to check for cache coherency

Subject: [PATCH] remap_file_pages needs to check for cache coherency
From: Matthew Wilcox <>
Date: Fri, 27 Dec 2013 13:00:18 -0500
Cc: "David S. Miller" <>,,,
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Original-recipient: rfc822;
User-agent: Mutt/1.5.21 (2010-09-15)
It seems to me that while (for example) on SPARC, it's not possible to
create a non-coherent mapping with mmap(), after we've done an mmap,
we can then use remap_file_pages() to create a mapping that no longer
aliases in the D-cache.

I have only compile-tested this patch.  I don't have any SPARC hardware,
and my PA-RISC hardware hasn't been turned on in six years ... I noticed
this while wandering around looking at some other stuff.

diff --git a/mm/fremap.c b/mm/fremap.c
index 5bff081..01fc2e7 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -19,6 +19,7 @@
 #include <asm/mmu_context.h>
 #include <asm/cacheflush.h>
+#include <asm/shmparam.h>
 #include <asm/tlbflush.h>
 #include "internal.h"
@@ -177,6 +178,13 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, 
unsigned long, size,
        if (start < vma->vm_start || start + size > vma->vm_end)
                goto out;
+       /* Is the mapping cache-coherent? */
+       if ((pgoff ^ linear_page_index(vma, start)) &
+           ((SHMLBA-1) >> PAGE_SHIFT))
+               goto out;
        /* Must set VM_NONLINEAR before any pages are populated. */
        if (!(vma->vm_flags & VM_NONLINEAR)) {

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