[3.8.y.z extended stable] Patch "arm64: vdso: fix coarse clock handling" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    arm64: vdso: fix coarse clock handling

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From d83d564a46c48a1758e0c8bc1d888fdbaf35b81c Mon Sep 17 00:00:00 2001
From: Nathan Lynch <nathan_lynch at mentor.com>
Date: Wed, 5 Feb 2014 05:53:04 +0000
Subject: arm64: vdso: fix coarse clock handling

commit 069b918623e1510e58dacf178905a72c3baa3ae4 upstream.

When __kernel_clock_gettime is called with a CLOCK_MONOTONIC_COARSE or
CLOCK_REALTIME_COARSE clock id, it returns incorrectly to whatever the
caller has placed in x2 ("ret x2" to return from the fast path).  Fix
this by saving x30/LR to x2 only in code that will call
__do_get_tspec, restoring x30 afterward, and using a plain "ret" to
return from the routine.

Also: while the resulting tv_nsec value for CLOCK_REALTIME and
CLOCK_MONOTONIC must be computed using intermediate values that are
left-shifted by cs_shift (x12, set by __do_get_tspec), the results for
coarse clocks should be calculated using unshifted values
(xtime_coarse_nsec is in units of actual nanoseconds).  The current
code shifts intermediate values by x12 unconditionally, but x12 is
uninitialized when servicing a coarse clock.  Fix this by setting x12
to 0 once we know we are dealing with a coarse clock id.

Signed-off-by: Nathan Lynch <nathan_lynch at mentor.com>
Acked-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm64/kernel/vdso/gettimeofday.S | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
index f0a6d10..fe652ff 100644
--- a/arch/arm64/kernel/vdso/gettimeofday.S
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -103,6 +103,8 @@ ENTRY(__kernel_clock_gettime)
 	bl	__do_get_tspec
 	seqcnt_check w9, 1b

+	mov	x30, x2
+
 	cmp	w0, #CLOCK_MONOTONIC
 	b.ne	6f

@@ -118,6 +120,9 @@ ENTRY(__kernel_clock_gettime)
 	ccmp	w0, #CLOCK_MONOTONIC_COARSE, #0x4, ne
 	b.ne	8f

+	/* xtime_coarse_nsec is already right-shifted */
+	mov	x12, #0
+
 	/* Get coarse timespec. */
 	adr	vdso_data, _vdso_data
 3:	seqcnt_acquire
@@ -156,7 +161,7 @@ ENTRY(__kernel_clock_gettime)
 	lsr	x11, x11, x12
 	stp	x10, x11, [x1, #TSPEC_TV_SEC]
 	mov	x0, xzr
-	ret	x2
+	ret
 7:
 	mov	x30, x2
 8:	/* Syscall fallback. */
--
1.8.3.2