linux-kernel - [PATCH v12 3/10] x86, asm: Change is_new_memtype

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Message-Id: <1433187393-22688-4-git-send-email-toshi.kani@hp.com>
Date:	Mon,  1 Jun 2015 13:36:26 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	bp@...en8.de, hpa@...or.com, tglx@...utronix.de, mingo@...hat.com,
	akpm@...ux-foundation.org, arnd@...db.de
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-nvdimm@...ts.01.org, jgross@...e.com,
	stefan.bader@...onical.com, luto@...capital.net, hmh@....eng.br,
	yigal@...xistor.com, konrad.wilk@...cle.com, Elliott@...com,
	mcgrof@...e.com, hch@....de, Toshi Kani <toshi.kani@...com>
Subject: [PATCH v12 3/10] x86, asm: Change is_new_memtype_allowed() for WT

__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@...com>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
---
 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;
 	}
 
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