This is a note to let you know that I've just added the patch titled

clocksource/drivers/arm_arch_timer: Validate CNTFRQ after enabling frame

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: clocksource-drivers-arm_arch_timer-validate-cntfrq-after-enabling-frame.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Wed Dec 6 18:04:41 CET 2017

From: Ard Biesheuvel ard.biesheuvel@linaro.org Date: Mon, 16 Oct 2017 16:28:38 +0100 Subject: clocksource/drivers/arm_arch_timer: Validate CNTFRQ after enabling frame

From: Ard Biesheuvel ard.biesheuvel@linaro.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@linaro.org Signed-off-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Daniel Lezcano daniel.lezcano@linaro.org Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.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;

Patches currently in stable-queue which might be from ard.biesheuvel@linaro.org are

queue-4.14/locking-refcounts-x86-asm-use-unique-.text-section-for-refcount-exceptions.patch queue-4.14/locking-refcounts-x86-asm-enable-config_arch_has_refcount.patch queue-4.14/clocksource-drivers-arm_arch_timer-validate-cntfrq-after-enabling-frame.patch