linux-kernel - [PATCH] x86/mm: avoid premature success when changing page attributes

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Message-Id: <56A6615E02000078000CAC96@prv-mh.provo.novell.com>
Date:	Mon, 25 Jan 2016 09:54:38 -0700
From:	"Jan Beulich" <JBeulich@...e.com>
To:	<mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/mm: avoid premature success when changing page
 attributes

Since successful return from __cpa_process_fault() makes
__change_page_attr() exit early (and successfully), its caller needs to
be instructed to continue its iteration by adjusting ->numpages. While
this already happens on one of __cpa_process_fault()'s successful exit
paths, the other needs this done similarly. This was in particular a
problem when the top level caller passed zero for "checkalias"
(becoming the "primary" value for the other two mentioned functions),
as is the case in change_page_attr_set_clr() when the OR of "mask_set"
and "mask_clr" equals _PAGE_NX, as e.g. passed from set_memory_{,n}x().

Signed-off-by: Jan Beulich <jbeulich@...e.com>
---
 arch/x86/mm/pageattr.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- 4.5-rc1/arch/x86/mm/pageattr.c
+++ 4.5-rc1-x86-cpa-non-primary/arch/x86/mm/pageattr.c
@@ -1122,8 +1122,10 @@ static int __cpa_process_fault(struct cp
 	/*
 	 * Ignore all non primary paths.
 	 */
-	if (!primary)
+	if (!primary) {
+		cpa->numpages = 1;
 		return 0;
+	}

 	/*
 	 * Ignore the NULL PTE for kernel identity mapping, as it is expected