On Thu, Sep 24, 2026 at 02:30:44PM +0200, Boris Brezillon wrote:
> We're trying to be smart by skipping the UPDATE(UNMAPPED) step, but
> it remains to be proven it adds any noticeable overhead. Moreover, it's
> breaking the assumption that, once the VM is unbound, no access can
> happen on it.
>
> For instance, say the panthor_mmu_as_enable() call in panthor_vm_active()
> fails after we've called panthor_vm_release_as_locked(), we're now in a
> state where the HW still points to the old page table, but SW slot points
> to the new VM, which is not truly HW-bound.
>
> If, after the as_slots lock is released, the evicted VM itself is
> released, the HW might have access to memory that has been returned
> to the system until the reset we scheduled (because of the faulty
> AS_COMMAND) is effective.
>
> Let's make this bullet-proof by doing a full bound -> unbound -> bound
> cycle on AS slot recycling.
>
> Fixes: 32e593d74c39 ("drm/panthor: Make sure caches are flushed/invalidated
> when an AS is recycled")
> Signed-off-by: Boris Brezillon <[email protected]>
Reviewed-by: Liviu Dudau <[email protected]>
Best regards,
Liviu
> ---
> drivers/gpu/drm/panthor/panthor_mmu.c | 21 +++++++--------------
> 1 file changed, 7 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c
> b/drivers/gpu/drm/panthor/panthor_mmu.c
> index 7e98084b9a1e..038a092fd08c 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -620,8 +620,7 @@ static int panthor_mmu_as_enable(struct panthor_device
> *ptdev, u32 as_nr,
> return as_send_cmd_and_wait(ptdev, as_nr, AS_COMMAND_UPDATE);
> }
>
> -static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 as_nr,
> - bool recycle_slot)
> +static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 as_nr)
> {
> struct panthor_mmu *mmu = ptdev->mmu;
> struct panthor_vm *vm = ptdev->mmu->as.slots[as_nr].vm;
> @@ -645,12 +644,6 @@ static int panthor_mmu_as_disable(struct panthor_device
> *ptdev, u32 as_nr,
> return ret;
> }
>
> - /* If the slot is going to be used immediately, don't bother changing
> - * the config.
> - */
> - if (recycle_slot)
> - return 0;
> -
> gpu_write64(mmu->iomem, AS_TRANSTAB(as_nr), 0);
> gpu_write64(mmu->iomem, AS_MEMATTR(as_nr), 0);
> gpu_write64(mmu->iomem, AS_TRANSCFG(as_nr),
> AS_TRANSCFG_ADRMODE_UNMAPPED);
> @@ -777,7 +770,7 @@ int panthor_vm_active(struct panthor_vm *vm)
> drm_WARN_ON(&ptdev->base,
> refcount_read(&lru_vm->as.active_cnt));
> as = lru_vm->as.id;
>
> - ret = panthor_mmu_as_disable(ptdev, as, true);
> + ret = panthor_mmu_as_disable(ptdev, as);
> if (ret)
> goto out_unlock;
>
> @@ -919,7 +912,7 @@ static void panthor_vm_declare_unusable(struct panthor_vm
> *vm)
> vm->unusable = true;
> mutex_lock(&ptdev->mmu->as.slots_lock);
> if (vm->as.id >= 0 && drm_dev_enter(&ptdev->base, &cookie)) {
> - panthor_mmu_as_disable(ptdev, vm->as.id, false);
> + panthor_mmu_as_disable(ptdev, vm->as.id);
> drm_dev_exit(cookie);
> }
> mutex_unlock(&ptdev->mmu->as.slots_lock);
> @@ -1911,7 +1904,7 @@ static void panthor_mmu_irq_handler(struct
> panthor_device *ptdev, u32 status)
> ptdev->mmu->as.slots[as].vm->unhandled_fault = true;
>
> /* Disable the MMU to kill jobs on this AS. */
> - panthor_mmu_as_disable(ptdev, as, false);
> + panthor_mmu_as_disable(ptdev, as);
> mutex_unlock(&ptdev->mmu->as.slots_lock);
>
> status &= ~mask;
> @@ -1940,7 +1933,7 @@ void panthor_mmu_suspend(struct panthor_device *ptdev)
>
> if (vm) {
> drm_WARN_ON(&ptdev->base,
> - panthor_mmu_as_disable(ptdev, i, false));
> + panthor_mmu_as_disable(ptdev, i));
> panthor_vm_release_as_locked(vm);
> }
> }
> @@ -2065,7 +2058,7 @@ static void panthor_vm_free(struct drm_gpuvm *gpuvm)
> int cookie;
>
> if (drm_dev_enter(&ptdev->base, &cookie)) {
> - panthor_mmu_as_disable(ptdev, vm->as.id, false);
> + panthor_mmu_as_disable(ptdev, vm->as.id);
> drm_dev_exit(cookie);
> }
>
> @@ -3360,7 +3353,7 @@ void panthor_mmu_unplug(struct panthor_device *ptdev)
>
> if (vm) {
> drm_WARN_ON(&ptdev->base,
> - panthor_mmu_as_disable(ptdev, i, false));
> + panthor_mmu_as_disable(ptdev, i));
> panthor_vm_release_as_locked(vm);
> }
> }
>
> --
> 2.55.0
>
--
====================
| I would like to |
| fix the world, |
| but they're not |
| giving me the |
\ source code! /
---------------
¯\_(ツ)_/¯
