[Intel-gfx] [RFC 2/5] drm/i915: Extract code mapping errno to vm fault code

[Chris Wilson]

On Tue, Jan 26, 2016 at 02:53:30PM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Will be used from multiple callers in a following patch.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 91 ++++++++++++++++++++++-------------------
>  1 file changed, 49 insertions(+), 42 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index af15c290c71d..dacf6a0013c5 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1772,6 +1772,53 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>  	return 0;
>  }
>  
> +static int
> +i915_gem_ret_to_vm_ret(struct drm_i915_private *dev_priv, int ret)
> +{
> +	switch (ret) {
> +	case -EIO:
> +		/*
> +		 * We eat errors when the gpu is terminally wedged to avoid
> +		 * userspace unduly crashing (gl has no provisions for mmaps to
> +		 * fail). But any other -EIO isn't ours (e.g. swap in failure)
> +		 * and so needs to be reported.
> +		 */
> +		if (!i915_terminally_wedged(&dev_priv->gpu_error)) {
> +			ret = VM_FAULT_SIGBUS;
> +			break;
> +		}
> +	case -EAGAIN:
> +		/*
> +		 * EAGAIN means the gpu is hung and we'll wait for the error
> +		 * handler to reset everything when re-faulting in
> +		 * i915_mutex_lock_interruptible.
> +		 */
> +	case 0:
> +	case -ERESTARTSYS:
> +	case -EINTR:
> +	case -EBUSY:
> +		/*
> +		 * EBUSY is ok: this just means that another thread
> +		 * already did the job.
> +		 */
> +		ret = VM_FAULT_NOPAGE;
> +		break;
> +	case -ENOMEM:
> +		ret = VM_FAULT_OOM;
> +		break;
> +	case -ENOSPC:
> +	case -EFAULT:
> +		ret = VM_FAULT_SIGBUS;
> +		break;
> +	default:
> +		WARN_ONCE(ret, "unhandled error in page fault\n");
> +		ret = VM_FAULT_SIGBUS;
> +		break;
> +	}

So without having to pin (plus a few other similar changes), we only need
to report

-ENOMEM, -ENOSPC, -EIO (from shmemfs) and -EFAULT (get_pages).

Given that I'd rather have the reasoning behind each explicit.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre