On 6/11/20 2:35 AM, Thomas Hellström (Intel) wrote:
On 6/10/20 11:19 PM, Andrey Grodzovsky wrote:
On 6/10/20 4:30 PM, Thomas Hellström (Intel) wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote:
Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey"
<Andrey.Grodzovsky@xxxxxxx>:
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@xxxxxxx>
>>>> ---
>>>> 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.
Can you explain more on this - specifically, which function to
reserve
the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but
we don't
need this because we unmap everything because the whole device is
gone and
not just manipulate a single BO.
So the device removed flag needs to be advertized before this
function is run,
I indeed intend to call this right after calling drm_dev_unplug
from
amdgpu_pci_remove while adding drm_dev_enter/exit in
ttm_bo_vm_fault (or
in amdgpu specific wrapper since I don't see how can I access struct
drm_device from ttm_bo_vm_fault) and this in my understanding should
stop a PTE from being re-faulted back as you pointed out - so
again I
don't see how bo reservation would prevent it so it looks like I am
missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I
don't think require any extra memory barriers for visibility of the
removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler.
Otherwise you're still open to the races Thomas described. But
aside from
that the drm_dev_unplug stuff has all the barriers and stuff to
make sure
nothing escapes.
Failure to drm_dev_enter could then also trigger the special case
where we
put a dummy page in place.
-Daniel
Hmm, Yes, indeed advertizing the flag before the call to
unmap_mapping_range isn't enough, since there might be fault
handlers running that haven't picked up the flag when
unmap_mapping_range is launched.
If you mean those fault handlers that were in progress when the flag
(drm_dev_unplug) was set in amdgpu_pci_remove then as long as i wrap
the entire fault handler (probably using amdgpu specific .fault hook
around ttm_bo_vm_fault) with drm_dev_enter/exit pair then
drm_dev_unplug->synchronize_srcu will block until those in progress
faults have completed and only after this i will call
unmap_mapping_range. Should this be enough ?
Andrey
Yes, I believe so. Although I suspect you might trip lockdep with
reverse locking order against the mmap_sem which is a constant pain in
fault handlers. If that's the case, you might be able to introduce
another srcu lock for this special purpose and synchronize just before
the address-space-wide unmap_mapping_range(). If it turns out that an
address space srcu lock like this is really needed, we should follow
Daniel's suggestion and try to use it from drm-wide helpers.
/Thomas
Does it make sense to prefault and set to zero page the entire VA range
covered by the given VMA on the first page fault post device disconnect
to save on other similar page faults ?
Andrey
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