linux-kernel - [PATCH 4.14 41/75] clocksource/drivers/arm_arch_timer: Validate CNTFRQ after enabling frame

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Date:   Thu,  7 Dec 2017 14:08:03 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.14 41/75] clocksource/drivers/arm_arch_timer: Validate CNTFRQ after enabling frame

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

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

From: Ard Biesheuvel <ard.biesheuvel@...aro.org>


[ Upstream commit 21492e1333a0d07af6968667f128e19088cf5ead ]

The ACPI GTDT code validates the CNTFRQ field of each MMIO timer
frame against the CNTFRQ system register of the current CPU, to
ensure that they are equal, which is mandated by the architecture.

However, reading the CNTFRQ field of a frame is not possible until
the RFRQ bit in the frame's CNTACRn register is set, and doing so
before that willl produce the following error:

  arch_timer: [Firmware Bug]: CNTFRQ mismatch: frame @ 0x00000000e0be0000: (0x00000000), CPU: (0x0ee6b280)
  arch_timer: Disabling MMIO timers due to CNTFRQ mismatch
  arch_timer: Failed to initialize memory-mapped timer.

The reason is that the CNTFRQ field is RES0 if access is not enabled.

So move the validation of CNTFRQ into the loop that iterates over the
timers to find the best frame, but defer it until after we have selected
the best frame, which should also have enabled the RFRQ bit.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Signed-off-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/clocksource/arm_arch_timer.c |   38 +++++++++++++++++++----------------
 1 file changed, 21 insertions(+), 17 deletions(-)

--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -1268,10 +1268,6 @@ arch_timer_mem_find_best_frame(struct ar
 
 	iounmap(cntctlbase);
 
-	if (!best_frame)
-		pr_err("Unable to find a suitable frame in timer @ %pa\n",
-			&timer_mem->cntctlbase);
-
 	return best_frame;
 }
 
@@ -1372,6 +1368,8 @@ static int __init arch_timer_mem_of_init
 
 	frame = arch_timer_mem_find_best_frame(timer_mem);
 	if (!frame) {
+		pr_err("Unable to find a suitable frame in timer @ %pa\n",
+			&timer_mem->cntctlbase);
 		ret = -EINVAL;
 		goto out;
 	}
@@ -1420,7 +1418,7 @@ arch_timer_mem_verify_cntfrq(struct arch
 static int __init arch_timer_mem_acpi_init(int platform_timer_count)
 {
 	struct arch_timer_mem *timers, *timer;
-	struct arch_timer_mem_frame *frame;
+	struct arch_timer_mem_frame *frame, *best_frame = NULL;
 	int timer_count, i, ret = 0;
 
 	timers = kcalloc(platform_timer_count, sizeof(*timers),
@@ -1432,14 +1430,6 @@ static int __init arch_timer_mem_acpi_in
 	if (ret || !timer_count)
 		goto out;
 
-	for (i = 0; i < timer_count; i++) {
-		ret = arch_timer_mem_verify_cntfrq(&timers[i]);
-		if (ret) {
-			pr_err("Disabling MMIO timers due to CNTFRQ mismatch\n");
-			goto out;
-		}
-	}
-
 	/*
 	 * While unlikely, it's theoretically possible that none of the frames
 	 * in a timer expose the combination of feature we want.
@@ -1448,12 +1438,26 @@ static int __init arch_timer_mem_acpi_in
 		timer = &timers[i];
 
 		frame = arch_timer_mem_find_best_frame(timer);
-		if (frame)
-			break;
+		if (!best_frame)
+			best_frame = frame;
+
+		ret = arch_timer_mem_verify_cntfrq(timer);
+		if (ret) {
+			pr_err("Disabling MMIO timers due to CNTFRQ mismatch\n");
+			goto out;
+		}
+
+		if (!best_frame) /* implies !frame */
+			/*
+			 * Only complain about missing suitable frames if we
+			 * haven't already found one in a previous iteration.
+			 */
+			pr_err("Unable to find a suitable frame in timer @ %pa\n",
+				&timer->cntctlbase);
 	}
 
-	if (frame)
-		ret = arch_timer_mem_frame_register(frame);
+	if (best_frame)
+		ret = arch_timer_mem_frame_register(best_frame);
 out:
 	kfree(timers);
 	return ret;