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

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Message-ID: <3582c630ee753db6ef1370612e69f36287536912.camel@imgtec.com>
Date:   Tue, 28 Nov 2023 10:47:19 +0000
From:   Donald Robson <Donald.Robson@...tec.com>
To:     "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>,
        "dakr@...hat.com" <dakr@...hat.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

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?

Many thanks,
Donald

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