On 2020-11-12 22:05, John Stultz wrote:
Robin Murphy pointed out that if the arm-smmu driver probes before
the qcom_scm driver, we may call qcom_scm_qsmmu500_wait_safe_toggle()
before the __scm is initialized.
Now, getting this to happen is a bit contrived, as in my efforts it
required enabling asynchronous probing for both drivers, moving the
firmware dts node to the end of the dtsi file, as well as forcing a
long delay in the qcom_scm_probe function.
With those tweaks we ran into the following crash:
[ 2.631040] arm-smmu 15000000.iommu: Stage-1: 48-bit VA -> 48-bit IPA
[ 2.633372] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
...
[ 2.633402] [0000000000000000] user address but active_mm is swapper
[ 2.633409] Internal error: Oops: 96000005 [#1] PREEMPT SMP
[ 2.633415] Modules linked in:
[ 2.633427] CPU: 5 PID: 117 Comm: kworker/u16:2 Tainted: G W 5.10.0-rc1-mainline-00025-g272a618fc36-dirty #3971
[ 2.633430] Hardware name: Thundercomm Dragonboard 845c (DT)
[ 2.633448] Workqueue: events_unbound async_run_entry_fn
[ 2.633456] pstate: 80c00005 (Nzcv daif +PAN +UAO -TCO BTYPE=--)
[ 2.633465] pc : qcom_scm_qsmmu500_wait_safe_toggle+0x78/0xb0
[ 2.633473] lr : qcom_smmu500_reset+0x58/0x78
[ 2.633476] sp : ffffffc0105a3b60
...
[ 2.633567] Call trace:
[ 2.633572] qcom_scm_qsmmu500_wait_safe_toggle+0x78/0xb0
[ 2.633576] qcom_smmu500_reset+0x58/0x78
[ 2.633581] arm_smmu_device_reset+0x194/0x270
[ 2.633585] arm_smmu_device_probe+0xc94/0xeb8
[ 2.633592] platform_drv_probe+0x58/0xa8
[ 2.633597] really_probe+0xec/0x398
[ 2.633601] driver_probe_device+0x5c/0xb8
[ 2.633606] __driver_attach_async_helper+0x64/0x88
[ 2.633610] async_run_entry_fn+0x4c/0x118
[ 2.633617] process_one_work+0x20c/0x4b0
[ 2.633621] worker_thread+0x48/0x460
[ 2.633628] kthread+0x14c/0x158
[ 2.633634] ret_from_fork+0x10/0x18
[ 2.633642] Code: a9034fa0 d0007f73 29107fa0 91342273 (f9400020)
To avoid this, this patch adds a check on qcom_scm_is_available() in
the qcom_smmu_impl_init() function, returning -EPROBE_DEFER if its
not ready.
This allows the driver to try to probe again later after qcom_scm has
finished probing.
As well as strict correctness, the other motivation here was that
qcom_scm_is_available() should be the place to add the "is the module
even loaded yet?" dance to iron out the awkward config dependencies in
future.
Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Andy Gross <agross@xxxxxxxxxx>
Cc: Maulik Shah <mkshah@xxxxxxxxxxxxxx>
Cc: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
Cc: Saravana Kannan <saravanak@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Lina Iyer <ilina@xxxxxxxxxxxxxx>
Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: linux-arm-msm <linux-arm-msm@xxxxxxxxxxxxxxx>
Reported-by: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
index 66ba4870659f4..ef37ccfa82562 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
@@ -159,6 +159,10 @@ struct arm_smmu_device *qcom_smmu_impl_init(struct arm_smmu_device *smmu)
{
struct qcom_smmu *qsmmu;
+ /* Check to make sure qcom_scm has finished probing */
+ if (!qcom_scm_is_available())
+ return ERR_PTR(-EPROBE_DEFER);
+
qsmmu = devm_kzalloc(smmu->dev, sizeof(*qsmmu), GFP_KERNEL);
if (!qsmmu)
return ERR_PTR(-ENOMEM);
