linux-kernel - Re: [EXTERNAL] [PATCH drm-misc-next 5/5] drm/imagination: vm: make use of GPUVM's drm

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Date:   Tue, 28 Nov 2023 20:02:05 +0100
From:   Danilo Krummrich <dakr@...hat.com>
To:     Donald Robson <Donald.Robson@...tec.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        Frank Binns <Frank.Binns@...tec.com>,
        Matt Coster <Matt.Coster@...tec.com>,
        "mripard@...nel.org" <mripard@...nel.org>,
        "airlied@...il.com" <airlied@...il.com>,
        Sarah Walker <Sarah.Walker@...tec.com>
Cc:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [EXTERNAL] [PATCH drm-misc-next 5/5] drm/imagination: vm: make
 use of GPUVM's drm_exec helper

On 11/28/23 11:47, Donald Robson wrote:
> Hi Danilo,
> 
> Apologies - I guess I should have submitted a patch to handle zero fences in your
> locking functions with the final patch series.
> 
> On Sat, 2023-11-25 at 00:36 +0100, Danilo Krummrich wrote:
>> *** CAUTION: This email originates from a source not known to Imagination Technologies. Think before you click a link or open an attachment ***
>>
>> Make use of GPUVM's drm_exec helper functions preventing direct access
>> to GPUVM internal data structures, such as the external object list.
>>
>> This is especially important to ensure following the locking rules
>> around the GPUVM external object list.
>>
>> Fixes: ff5f643de0bf ("drm/imagination: Add GEM and VM related code")
>> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
>> ---
>>   drivers/gpu/drm/imagination/pvr_vm.c | 16 +++++-----------
>>   1 file changed, 5 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/imagination/pvr_vm.c b/drivers/gpu/drm/imagination/pvr_vm.c
>> index e0d74d9a6190..3f7888f5cc53 100644
>> --- a/drivers/gpu/drm/imagination/pvr_vm.c
>> +++ b/drivers/gpu/drm/imagination/pvr_vm.c
>> @@ -337,27 +337,21 @@ static int
>>   pvr_vm_bind_op_lock_resvs(struct drm_exec *exec, struct pvr_vm_bind_op *bind_op)
>>   {
>>   	drm_exec_until_all_locked(exec) {
>> -		struct drm_gem_object *r_obj = &bind_op->vm_ctx->dummy_gem;
>>   		struct drm_gpuvm *gpuvm = &bind_op->vm_ctx->gpuvm_mgr;
>>   		struct pvr_gem_object *pvr_obj = bind_op->pvr_obj;
>> -		struct drm_gpuvm_bo *gpuvm_bo;
>>   
>>   		/* Acquire lock on the vm_context's reserve object. */
>> -		int err = drm_exec_lock_obj(exec, r_obj);
>> +		int err = drm_gpuvm_prepare_vm(gpuvm, exec, 0);
>>   
>>   		drm_exec_retry_on_contention(exec);
>>   		if (err)
>>   			return err;
>>   
>>   		/* Acquire lock on all BOs in the context. */
>> -		list_for_each_entry(gpuvm_bo, &gpuvm->extobj.list,
>> -				    list.entry.extobj) {
>> -			err = drm_exec_lock_obj(exec, gpuvm_bo->obj);
>> -
>> -			drm_exec_retry_on_contention(exec);
>> -			if (err)
>> -				return err;
>> -		}
>> +		err = drm_gpuvm_prepare_objects(gpuvm, exec, 0);
>> +		drm_exec_retry_on_contention(exec);
>> +		if (err)
>> +			return err;
> 
> Before I discovered the problem when not reserving fences, I was trying to use
> drm_gpuvm_exec_lock() with vm_exec->extra.fn() for the part below.  Is there
> a reason not to do that now?

No, that works - gonna change that.

- Danilo

> 
> Many thanks,
> Donald
> 
>>   
>>   		/* Unmap operations don't have an object to lock. */
>>   		if (!pvr_obj)