[Intel-gfx] [PATCH 5/6] drm/i915: Support for pread/pwrite from/to non shmem backed objects

[Dave Gordon]

On 10/12/15 11:12, Ankitprasad Sharma wrote:
> On Wed, 2015-12-09 at 19:39 +0000, Dave Gordon wrote:
>> On 09/12/15 16:15, Tvrtko Ursulin wrote:
>>>
>>> Hi,
>>>
>>> On 09/12/15 12:46, ankitprasad.r.sharma at intel.com wrote:
>>>> From: Ankitprasad Sharma <ankitprasad.r.sharma at intel.com>
>>>>
>>>> This patch adds support for extending the pread/pwrite functionality
>>>> for objects not backed by shmem. The access will be made through
>>>> gtt interface. This will cover objects backed by stolen memory as well
>>>> as other non-shmem backed objects.
>>>>
>>>> v2: Drop locks around slow_user_access, prefault the pages before
>>>> access (Chris)
>>>>
>>>> v3: Rebased to the latest drm-intel-nightly (Ankit)
>>>>
>>>> v4: Moved page base & offset calculations outside the copy loop,
>>>> corrected data types for size and offset variables, corrected if-else
>>>> braces format (Tvrtko/kerneldocs)
>>>>
>>>> v5: Enabled pread/pwrite for all non-shmem backed objects including
>>>> without tiling restrictions (Ankit)
>>>>
>>>> v6: Using pwrite_fast for non-shmem backed objects as well (Chris)
>>>>
>>>> v7: Updated commit message, Renamed i915_gem_gtt_read to
>>>> i915_gem_gtt_copy,
>>>> added pwrite slow path for non-shmem backed objects (Chris/Tvrtko)
>>>>
>>>> v8: Updated v7 commit message, mutex unlock around pwrite slow path for
>>>> non-shmem backed objects (Tvrtko)
>>>>
>>>> Testcase: igt/gem_stolen
>>>>
>>>> Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma at intel.com>
>>>> ---
>>>>    drivers/gpu/drm/i915/i915_gem.c | 151
>>>> +++++++++++++++++++++++++++++++++-------
>>>>    1 file changed, 127 insertions(+), 24 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/i915_gem.c
>>>> b/drivers/gpu/drm/i915/i915_gem.c
>>>> index ed97de6..68ed67a 100644
>>>> --- a/drivers/gpu/drm/i915/i915_gem.c
>>>> +++ b/drivers/gpu/drm/i915/i915_gem.c
>>>> @@ -614,6 +614,99 @@ shmem_pread_slow(struct page *page, int
>>>> shmem_page_offset, int page_length,
>>>>        return ret ? - EFAULT : 0;
>>>>    }
>>>>
>>>> +static inline uint64_t
>>>> +slow_user_access(struct io_mapping *mapping,
>>>> +         uint64_t page_base, int page_offset,
>>>> +         char __user *user_data,
>>>> +         int length, bool pwrite)
>>>> +{
>>>> +    void __iomem *vaddr_inatomic;
>>>> +    void *vaddr;
>>>> +    uint64_t unwritten;
>>>> +
>>>> +    vaddr_inatomic = io_mapping_map_wc(mapping, page_base);
>>>> +    /* We can use the cpu mem copy function because this is X86. */
>>>> +    vaddr = (void __force *)vaddr_inatomic + page_offset;
>>>> +    if (pwrite)
>>>> +        unwritten = __copy_from_user(vaddr, user_data, length);
>>>> +    else
>>>> +        unwritten = __copy_to_user(user_data, vaddr, length);
>>>> +
>>>> +    io_mapping_unmap(vaddr_inatomic);
>>>> +    return unwritten;
>>>> +}
>>>> +
>>>> +static int
>>>> +i915_gem_gtt_copy(struct drm_device *dev,
>>>> +           struct drm_i915_gem_object *obj, uint64_t size,
>>>> +           uint64_t data_offset, uint64_t data_ptr)
>>>> +{
>>>> +    struct drm_i915_private *dev_priv = dev->dev_private;
>>>> +    char __user *user_data;
>>>> +    uint64_t remain;
>>>> +    uint64_t offset, page_base;
>>>> +    int page_offset, page_length, ret = 0;
>>>> +
>>>> +    ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
>>>> +    if (ret)
>>>> +        goto out;
>>>> +
>>>> +    ret = i915_gem_object_set_to_gtt_domain(obj, false);
>>>> +    if (ret)
>>>> +        goto out_unpin;
>>>> +
>>>> +    ret = i915_gem_object_put_fence(obj);
>>>> +    if (ret)
>>>> +        goto out_unpin;
>>>> +
>>>> +    user_data = to_user_ptr(data_ptr);
>>>> +    remain = size;
>>>> +    offset = i915_gem_obj_ggtt_offset(obj) + data_offset;
>>>> +
>>>> +    mutex_unlock(&dev->struct_mutex);
>>>> +    if (likely(!i915.prefault_disable))
>>>> +        ret = fault_in_multipages_writeable(user_data, remain);
>>>> +
>>>> +    /*
>>>> +     * page_offset = offset within page
>>>> +     * page_base = page offset within aperture
>>>> +     */
>>>> +    page_offset = offset_in_page(offset);
>>>> +    page_base = offset & PAGE_MASK;
>>>> +
>>>> +    while (remain > 0) {
>>>> +        /* page_length = bytes to copy for this page */
>>>> +        page_length = remain;
>>>> +        if ((page_offset + remain) > PAGE_SIZE)
>>>> +            page_length = PAGE_SIZE - page_offset;
>>>> +
>>>> +        /* This is a slow read/write as it tries to read from
>>>> +         * and write to user memory which may result into page
>>>> +         * faults
>>>> +         */
>>>> +        ret = slow_user_access(dev_priv->gtt.mappable, page_base,
>>>> +                       page_offset, user_data,
>>>> +                       page_length, false);
>>>> +
>>>> +        if (ret) {
>>>> +            ret = -EFAULT;
>>>> +            break;
>>>> +        }
>>>> +
>>>> +        remain -= page_length;
>>>> +        user_data += page_length;
>>>> +        page_base += page_length;
>>>> +        page_offset = 0;
>>>> +    }
>>>> +
>>>> +    mutex_lock(&dev->struct_mutex);
>>>> +
>>>> +out_unpin:
>>>> +    i915_gem_object_ggtt_unpin(obj);
>>>> +out:
>>>> +    return ret;
>>>> +}
>>>> +
>>>>    static int
>>>>    i915_gem_shmem_pread(struct drm_device *dev,
>>>>                 struct drm_i915_gem_object *obj,
>>>> @@ -737,17 +830,14 @@ i915_gem_pread_ioctl(struct drm_device *dev,
>>>> void *data,
>>>>            goto out;
>>>>        }
>>>>
>>>> -    /* prime objects have no backing filp to GEM pread/pwrite
>>>> -     * pages from.
>>>> -     */
>>>> -    if (!obj->base.filp) {
>>>> -        ret = -EINVAL;
>>>> -        goto out;
>>>> -    }
>>>> -
>>>>        trace_i915_gem_object_pread(obj, args->offset, args->size);
>>>>
>>>> -    ret = i915_gem_shmem_pread(dev, obj, args, file);
>>>> +    /* pread for non shmem backed objects */
>>>> +    if (!obj->base.filp && obj->tiling_mode == I915_TILING_NONE)
>>>> +        ret = i915_gem_gtt_copy(dev, obj, args->size,
>>>> +                    args->offset, args->data_ptr);
>>>> +    else
>>>> +        ret = i915_gem_shmem_pread(dev, obj, args, file);
>>>
>>> Hm, it will end up calling i915_gem_shmem_pread for non-shmem backed
>>> objects if tiling is set. Sounds wrong to me unless I am missing something?
>>
>> Which GEM objects have obj->base.filp set? Is it ONLY regular gtt-type
>> objects? What about (phys, stolen, userptr, dmabuf, ...?) Which of these
>> is the alternate path going to work with?
> Only shmem backed objects have obj->base.filp set, filp pointing to the
> shmem file. For all other non-shmem backed objects (stolen, userptr,
> dmabuf) we use the alternate path.
>
> -Ankit

But 'phys' objects DO have 'filp' set. Which path is expected to work 
for them?

.Dave.