[PATCH v9 3/10] x86, asm: Change is_new_memtype_allowed() for WT

From: Toshi Kani
Date: Wed May 13 2015 - 17:27:33 EST


__ioremap_caller() calls reserve_memtype() to set new_pcm
(existing map type if any), and then calls
is_new_memtype_allowed() to verify if converting to new_pcm
is allowed when pcm (request type) is different from new_pcm.

When WT is requested, the caller expects that writes are
ordered and uncached. Therefore, this patch changes
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>
---
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 fe57e7a..2562e30 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;
}

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/