Describe CVE-2021-47025.
What is CVE-2021-47025?
In the Linux kernel, the following vulnerability has been resolved:

iommu/mediatek: Always enable the clk on resume

In mtk_iommu_runtime_resume always enable the clk, even
if m4u_dom is null. Otherwise the 'suspend' cb might
disable the clk which is already disabled causing the warning:

[    1.586104] infra_m4u already disabled
[    1.586133] WARNING: CPU: 0 PID: 121 at drivers/clk/clk.c:952 clk_core_disable+0xb0/0xb8
[    1.594391] mtk-iommu 10205000.iommu: bound 18001000.larb (ops mtk_smi_larb_component_ops)
[    1.598108] Modules linked in:
[    1.598114] CPU: 0 PID: 121 Comm: kworker/0:2 Not tainted 5.12.0-rc5 #69
[    1.609246] mtk-iommu 10205000.iommu: bound 14027000.larb (ops mtk_smi_larb_component_ops)
[    1.617487] Hardware name: Google Elm (DT)
[    1.617491] Workqueue: pm pm_runtime_work
[    1.620545] mtk-iommu 10205000.iommu: bound 19001000.larb (ops mtk_smi_larb_component_ops)

[    1.627229] pstate: 60000085 (nZCv daIf -PAN -UAO -TCO BTYPE=--)
[    1.659297] pc : clk_core_disable+0xb0/0xb8
[    1.663475] lr : clk_core_disable+0xb0/0xb8
[    1.667652] sp : ffff800011b9bbe0
[    1.670959] x29: ffff800011b9bbe0 x28: 0000000000000000
[    1.676267] x27: ffff800011448000 x26: ffff8000100cfd98
[    1.681574] x25: ffff800011b9bd48 x24: 0000000000000000
[    1.686882] x23: 0000000000000000 x22: ffff8000106fad90
[    1.692189] x21: 000000000000000a x20: ffff0000c0048500
[    1.697496] x19: ffff0000c0048500 x18: ffffffffffffffff
[    1.702804] x17: 0000000000000000 x16: 0000000000000000
[    1.708112] x15: ffff800011460300 x14: fffffffffffe0000
[    1.713420] x13: ffff8000114602d8 x12: 0720072007200720
[    1.718727] x11: 0720072007200720 x10: 0720072007200720
[    1.724035] x9 : ffff800011b9bbe0 x8 : ffff800011b9bbe0
[    1.729342] x7 : 0000000000000009 x6 : ffff8000114b8328
[    1.734649] x5 : 0000000000000000 x4 : 0000000000000000
[    1.739956] x3 : 00000000ffffffff x2 : ffff800011460298
[    1.745263] x1 : 1af1d7de276f4500 x0 : 0000000000000000
[    1.750572] Call trace:
[    1.753010]  clk_core_disable+0xb0/0xb8
[    1.756840]  clk_core_disable_lock+0x24/0x40
[    1.761105]  clk_disable+0x20/0x30
[    1.764501]  mtk_iommu_runtime_suspend+0x88/0xa8
[    1.769114]  pm_generic_runtime_suspend+0x2c/0x48
[    1.773815]  __rpm_callback+0xe0/0x178
[    1.777559]  rpm_callback+0x24/0x88
[    1.781041]  rpm_suspend+0xdc/0x470
[    1.784523]  rpm_idle+0x12c/0x170
[    1.787831]  pm_runtime_work+0xa8/0xc0
[    1.791573]  process_one_work+0x1e8/0x360
[    1.795580]  worker_thread+0x44/0x478
[    1.799237]  kthread+0x150/0x158
[    1.802460]  ret_from_fork+0x10/0x30
[    1.806034] ---[ end trace 82402920ef64573b ]---
[    1.810728] ------------[ cut here ]------------

In addition, we now don't need to enable the clock from the
function mtk_iommu_hw_init since it is already enabled by the resume..