[tip:mm/pkeys] x86/pkeys: Add fault handling for PF_PK page fault bit

[tip-bot for Dave Hansen]

Commit-ID:  e8c6226d483cb28f55cab718065ea1b7226d40e8
Gitweb:     http://git.kernel.org/tip/e8c6226d483cb28f55cab718065ea1b7226d40e8
Author:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
AuthorDate: Fri, 29 Jul 2016 09:30:10 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 9 Sep 2016 13:02:26 +0200

x86/pkeys: Add fault handling for PF_PK page fault bit

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@xxxxxxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: arnd@xxxxxxxx
Cc: linux-api@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: luto@xxxxxxxxxx
Cc: akpm@xxxxxxxxxxxxxxxxxxxx
Cc: torvalds@xxxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20160729163010.DD1FE1ED@xxxxxxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

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

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index dc80230..b88d8ac 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1112,6 +1112,15 @@ access_error(unsigned long error_code, struct vm_area_struct *vma)
 {
 	/* 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