linux-kernel - [PATCH 01/10] x86, pkeys: add fault handling for PF

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Message-Id: <20160729163010.DD1FE1ED@viggo.jf.intel.com>
Date:	Fri, 29 Jul 2016 09:30:10 -0700
From:	Dave Hansen <dave@...1.net>
To:	linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, linux-api@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-mm@...ck.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	luto@...nel.org, mgorman@...hsingularity.net,
	Dave Hansen <dave@...1.net>, dave.hansen@...ux.intel.com,
	arnd@...db.de
Subject: [PATCH 01/10] x86, pkeys: add fault handling for PF_PK page fault bit


From: Dave Hansen <dave.hansen@...ux.intel.com>

PF_PK means that a memory access violated the protection key
access restrictions.  It is unconditionally an access_error()
because the permissions set on the VMA don't matter (the PKRU
value overrides it), and we never "resolve" PK faults (like
how a COW can "resolve write fault).

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Acked-by: Mel Gorman <mgorman@...hsingularity.net>
Cc: linux-api@...r.kernel.org
Cc: linux-arch@...r.kernel.org
Cc: linux-mm@...ck.org
Cc: x86@...nel.org
Cc: torvalds@...ux-foundation.org
Cc: akpm@...ux-foundation.org
Cc: Arnd Bergmann <arnd@...db.de>
---

 b/arch/x86/mm/fault.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff -puN arch/x86/mm/fault.c~pkeys-105-add-pk-to-fault arch/x86/mm/fault.c
--- a/arch/x86/mm/fault.c~pkeys-105-add-pk-to-fault	2016-07-29 09:18:55.920448993 -0700
+++ b/arch/x86/mm/fault.c	2016-07-29 09:18:55.923449129 -0700
@@ -1112,6 +1112,15 @@ access_error(unsigned long error_code, s
 {
 	/* This is only called for the current mm, so: */
 	bool foreign = false;
+
+	/*
+	 * Read or write was blocked by protection keys.  This is
+	 * always an unconditional error and can never result in
+	 * a follow-up action to resolve the fault, like a COW.
+	 */
+	if (error_code & PF_PK)
+		return 1;
+
 	/*
 	 * Make sure to check the VMA so that we do not perform
 	 * faults just to hit a PF_PK as soon as we fill in a
_