drm/amdgpu: Replace Mutex with Spinlock for RLCG register access to avoid Priority Inversion in SRIOV

In the Linux kernel, the following vulnerability has been resolved:

drm/amdgpu: Replace Mutex with Spinlock for RLCG register access to avoid Priority Inversion in SRIOV

RLCG Register Access is a way for virtual functions to safely access GPU

registers in a virtualized environment., including TLB flushes and

register reads. When multiple threads or VFs try to access the same

registers simultaneously, it can lead to race conditions. By using the

RLCG interface, the driver can serialize access to the registers. This

means that only one thread can access the registers at a time,

preventing conflicts and ensuring that operations are performed

correctly. Additionally, when a low-priority task holds a mutex that a

high-priority task needs, ie., If a thread holding a spinlock tries to

acquire a mutex, it can lead to priority inversion. register access in

amdgpu_virt_rlcg_reg_rw especially in a fast code path is critical.

The call stack shows that the function amdgpu_virt_rlcg_reg_rw is being

called, which attempts to acquire the mutex. This function is invoked

from amdgpu_sriov_wreg, which in turn is called from

gmc_v11_0_flush_gpu_tlb.

The [ BUG: Invalid wait context ] indicates that a thread is trying to

acquire a mutex while it is in a context that does not allow it to sleep

(like holding a spinlock).

Fixes the below:

[ 253.013423] =============================

[ 253.013434] [ BUG: Invalid wait context ]

[ 253.013446] 6.12.0-amdstaging-drm-next-lol-050225 #14 Tainted: G U OE

[ 253.013464] -----------------------------

[ 253.013475] kworker/0:1/10 is trying to lock:

[ 253.013487] ffff9f30542e3cf8 (&adev->virt.rlcg_reg_lock){+.+.}-{3:3}, at: amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]

[ 253.013815] other info that might help us debug this:

[ 253.013827] context-{4:4}

[ 253.013835] 3 locks held by kworker/0:1/10:

[ 253.013847] #0: ffff9f3040050f58 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x3f5/0x680

[ 253.013877] #1: ffffb789c008be40 ((work_completion)(&wfc.work)){+.+.}-{0:0}, at: process_one_work+0x1d6/0x680

[ 253.013905] #2: ffff9f3054281838 (&adev->gmc.invalidate_lock){+.+.}-{2:2}, at: gmc_v11_0_flush_gpu_tlb+0x198/0x4f0 [amdgpu]

[ 253.014154] stack backtrace:

[ 253.014164] CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Tainted: G U OE 6.12.0-amdstaging-drm-next-lol-050225 #14

[ 253.014189] Tainted: [U]=USER, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE

[ 253.014203] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 11/18/2024

[ 253.014224] Workqueue: events work_for_cpu_fn

[ 253.014241] Call Trace:

[ 253.014250] <TASK>

[ 253.014260] dump_stack_lvl+0x9b/0xf0

[ 253.014275] dump_stack+0x10/0x20

[ 253.014287] __lock_acquire+0xa47/0x2810

[ 253.014303] ? srso_alias_return_thunk+0x5/0xfbef5

[ 253.014321] lock_acquire+0xd1/0x300

[ 253.014333] ? amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]

[ 253.014562] ? __lock_acquire+0xa6b/0x2810

[ 253.014578] __mutex_lock+0x85/0xe20

[ 253.014591] ? amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]

[ 253.014782] ? sched_clock_noinstr+0x9/0x10

[ 253.014795] ? srso_alias_return_thunk+0x5/0xfbef5

[ 253.014808] ? local_clock_noinstr+0xe/0xc0

[ 253.014822] ? amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]

[ 253.015012] ? srso_alias_return_thunk+0x5/0xfbef5

[ 253.015029] mutex_lock_nested+0x1b/0x30

[ 253.015044] ? mutex_lock_nested+0x1b/0x30

[ 253.015057] amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]

[ 253.015249] amdgpu_sriov_wreg+0xc5/0xd0 [amdgpu]

[ 253.015435] gmc_v11_0_flush_gpu_tlb+0x44b/0x4f0 [amdgpu]

[ 253.015667] gfx_v11_0_hw_init+0x499/0x29c0 [amdgpu]

[ 253.015901] ? __pfx_smu_v13_0_update_pcie_parameters+0x10/0x10 [amdgpu]

[ 253.016159] ? srso_alias_return_thunk+0x5/0xfbef5

[ 253.016173] ? smu_hw_init+0x18d/0x300 [amdgpu]

[ 253.016403] amdgpu_device_init+0x29ad/0x36a0 [amdgpu]

[ 253.016614] amdgpu_driver_load_kms+0x1a/0xc0 [amdgpu]

[ 253.0170

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