[PATCH 06/20] x86/mm: Teach is_new_memtype_allowed() about Write-Through type

[Borislav Petkov]

From: Toshi Kani <toshi.kani@xxxxxx>

__ioremap_caller() calls reserve_memtype() and the passed down @new_pcm
contains the actual page cache type it reserved in the success case.

is_new_memtype_allowed() verifies if converting to the new page cache
type is allowed when @pcm (the requested type) is different from
@new_pcm.

When WT is requested, the caller expects that writes are ordered and
uncached. Therefore, enhance is_new_memtype_allowed() to disallow the
following cases:

 - If the request is WT, mapping type cannot be WB
 - If the request is WT, mapping type cannot be WC

Signed-off-by: Toshi Kani <toshi.kani@xxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: arnd@xxxxxxxx
Cc: Elliott@xxxxxx
Cc: hch@xxxxxx
Cc: hmh@xxxxxxxxxx
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: jgross@xxxxxxxx
Cc: konrad.wilk@xxxxxxxxxx
Cc: linux-mm <linux-mm@xxxxxxxxx>
Cc: linux-nvdimm@xxxxxxxxxxxx
Cc: Luis R. Rodriguez <mcgrof@xxxxxxxx>
Cc: stefan.bader@xxxxxxxxxxxxx
Cc: x86-ml <x86@xxxxxxxxxx>
Cc: yigal@xxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1433187393-22688-4-git-send-email-toshi.kani@xxxxxx
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/include/asm/pgtable.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index fe57e7a98839..2562e303405b 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -398,11 +398,17 @@ static inline int is_new_memtype_allowed(u64 paddr, unsigned long size,
 	 * requested memtype:
 	 * - request is uncached, return cannot be write-back
 	 * - request is write-combine, return cannot be write-back
+	 * - request is write-through, return cannot be write-back
+	 * - request is write-through, return cannot be write-combine
 	 */
 	if ((pcm == _PAGE_CACHE_MODE_UC_MINUS &&
 	     new_pcm == _PAGE_CACHE_MODE_WB) ||
 	    (pcm == _PAGE_CACHE_MODE_WC &&
-	     new_pcm == _PAGE_CACHE_MODE_WB)) {
+	     new_pcm == _PAGE_CACHE_MODE_WB) ||
+	    (pcm == _PAGE_CACHE_MODE_WT &&
+	     new_pcm == _PAGE_CACHE_MODE_WB) ||
+	    (pcm == _PAGE_CACHE_MODE_WT &&
+	     new_pcm == _PAGE_CACHE_MODE_WC)) {
 		return 0;
 	}
 
-- 
2.3.5

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