linux-kernel - [PATCH 3.11 028/121] arm64: vdso: fix coarse clock handling

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Message-Id: <1392986945-9693-29-git-send-email-luis.henriques@canonical.com>
Date:	Fri, 21 Feb 2014 12:47:32 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Nathan Lynch <nathan_lynch@...tor.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.11 028/121] arm64: vdso: fix coarse clock handling

3.11.10.5 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nathan Lynch <nathan_lynch@...tor.com>

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@...tor.com>
Acked-by: Will Deacon <will.deacon@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.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. */
-- 
1.9.0

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