In the Linux kernel, the following vulnerability has been resolved:
LoongArch: Define the _ioaw() hook as mmiowb()
Commit fb24ea52f78e0d595852e ("drivers: Remove explicit invocations of mmiowb()") remove all mmiowb() in drivers, but it says:
"NOTE: mmiowb() has only ever guaranteed ordering in conjunction with spinunlock(). However, pairing each mmiowb() removal in this patch with the corresponding call to spinunlock() is not at all trivial, so there is a small chance that this change may regress any drivers incorrectly relying on mmiowb() to order MMIO writes between CPUs using lock-free synchronisation."
The mmio in radeonringcommit() is protected by a mutex rather than a spinlock, but in the mutex fastpath it behaves similar to spinlock. We can add mmiowb() calls in the radeon driver but the maintainer says he doesn't like such a workaround, and radeon is not the only example of mutex protected mmio.
So we should extend the mmiowb tracking system from spinlock to mutex, and maybe other locking primitives. This is not easy and error prone, so we solve it in the architectural code, by simply defining the _ioaw() hook as mmiowb(). And we no longer need to override queuedspinunlock() so use the generic definition.
Without this, we get such an error when run 'glxgears' on weak ordering architectures such as LoongArch:
radeon 0000:04:00.0: ring 0 stalled for more than 10324msec radeon 0000:04:00.0: ring 3 stalled for more than 10240msec radeon 0000:04:00.0: GPU lockup (current fence id 0x000000000001f412 last fence id 0x000000000001f414 on ring 3) radeon 0000:04:00.0: GPU lockup (current fence id 0x000000000000f940 last fence id 0x000000000000f941 on ring 0) radeon 0000:04:00.0: scheduling IB failed (-35). [drm:radeongemvaioctl [radeon]] *ERROR* Couldn't update BOVA (-35) radeon 0000:04:00.0: scheduling IB failed (-35). [drm:radeongemvaioctl [radeon]] *ERROR* Couldn't update BOVA (-35) radeon 0000:04:00.0: scheduling IB failed (-35). [drm:radeongemvaioctl [radeon]] *ERROR* Couldn't update BOVA (-35) radeon 0000:04:00.0: scheduling IB failed (-35). [drm:radeongemvaioctl [radeon]] *ERROR* Couldn't update BOVA (-35) radeon 0000:04:00.0: scheduling IB failed (-35). [drm:radeongemvaioctl [radeon]] *ERROR* Couldn't update BOVA (-35) radeon 0000:04:00.0: scheduling IB failed (-35). [drm:radeongemvaioctl [radeon]] *ERROR* Couldn't update BOVA (-35) radeon 0000:04:00.0: scheduling IB failed (-35). [drm:radeongemvaioctl [radeon]] *ERROR* Couldn't update BOVA (-35)