[PATCH 1/6] drm/ttm: Add unampping of the entire device address space

[Thomas Hellström (Intel)]

On 6/9/20 7:21 PM, Koenig, Christian wrote:
>
>
> Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" 
> <Andrey.Grodzovsky at amd.com>:
>
>
>     On 6/5/20 2:40 PM, Christian König wrote:
>     > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky:
>     >>
>     >> On 5/11/20 2:45 AM, Christian König wrote:
>     >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky:
>     >>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
>     >>>> ---
>     >>>> drivers/gpu/drm/ttm/ttm_bo.c    | 22 +++++++++++++++++++++-
>     >>>> include/drm/ttm/ttm_bo_driver.h |  2 ++
>     >>>>   2 files changed, 23 insertions(+), 1 deletion(-)
>     >>>>
>     >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c
>     >>>> b/drivers/gpu/drm/ttm/ttm_bo.c
>     >>>> index c5b516f..eae61cc 100644
>     >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>     >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>     >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct
>     >>>> ttm_buffer_object *bo)
>     >>>> ttm_bo_unmap_virtual_locked(bo);
>     >>>>       ttm_mem_io_unlock(man);
>     >>>>   }
>     >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual);
>     >>>>   +void ttm_bo_unmap_virtual_address_space(struct
>     ttm_bo_device *bdev)
>     >>>> +{
>     >>>> +    struct ttm_mem_type_manager *man;
>     >>>> +    int i;
>     >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual);
>     >>>
>     >>>> +    for (i = 0; i < TTM_NUM_MEM_TYPES; i++) {
>     >>>> +        man = &bdev->man[i];
>     >>>> +        if (man->has_type && man->use_type)
>     >>>> + ttm_mem_io_lock(man, false);
>     >>>> +    }
>     >>>
>     >>> You should drop that it will just result in a deadlock warning
>     for
>     >>> Nouveau and has no effect at all.
>     >>>
>     >>> Apart from that looks good to me,
>     >>> Christian.
>     >>
>     >>
>     >> As I am considering to re-include this in V2 of the patchsets, can
>     >> you clarify please why this will have no effect at all ?
>     >
>     > The locks are exclusive for Nouveau to allocate/free the io address
>     > space.
>     >
>     > Since we don't do this here we don't need the locks.
>     >
>     > Christian.
>
>
>     So basically calling unmap_mapping_range doesn't require any extra
>     locking around it and whatever locks are taken within the function
>     should be enough ?
>
>
>
> I think so, yes.
>
> Christian.

Yes, that's true. However, without the bo reservation, nothing stops a 
PTE from being immediately re-faulted back again. Even while 
unmap_mapping_range() is running. So the device removed flag needs to be 
advertized before this function is run, (perhaps with a memory barrier 
pair). That should probably be added to the function documentation.

(Other than that, please add a commit message if respinning).

/Thomas



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