On Fri, Sep 6, 2019 at 2:13 PM Gerd Hoffmann kraxel@redhat.com wrote:
Hi,
I think if we do an mmap callback, it should replace all the mmap handling (except the drm_gem_object_get) that drm_gem_mmap_obj does. So maybe something like the below:
[ snip ]
Since I remember quite a few discussions where the default vma flag wrangling we're doing is seriously getting in the way of things too.
Yep, makes sense.
I think even better would be if this new ->mmap hook could also be used directly by the dma-buf mmap code, without having to jump through hoops creating a fake file and fake vma offset and everything. I think with that we'd have a really solid case to add this ->mmap hook.
Looks easy on a quick glance. So something like the patch below (quick sketch, not tested yet other than compiling it)?
Yup, looks good, and if it works I'm happy to smash r-b and a-b tags over this.
One thought below.
cheers, Gerd
From c13b30d776fb593a03473fa3bc93baf470cba728 Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann kraxel@redhat.com Date: Wed, 19 Jun 2019 14:26:51 +0200 Subject: [PATCH] drm: add mmap() to drm_gem_object_funcs
drm_gem_object_funcs->vm_ops alone can't handle everything which needs to be done for mmap(), tweaking vm_flags for example. So add a new mmap() callback to drm_gem_object_funcs where this code can go to.
Note that the vm_ops field is not used in case the mmap callback is presnt, it is expected that the callback sets vma->vm_ops instead.
drm_gem_mmap_obj() will use the new callback for object specific mmap setup. With this in place the need for driver-speific fops->mmap callbacks goes away, drm_gem_mmap can be hooked instead.
drm_gem_prime_mmap() will use the new callback too to just mmap gem objects directly instead of jumping though loops to make drm_gem_object_lookup() and fops->mmap work.
Signed-off-by: Gerd Hoffmann kraxel@redhat.com
include/drm/drm_gem.h | 14 ++++++++++++++ drivers/gpu/drm/drm_gem.c | 26 +++++++++++++++++--------- drivers/gpu/drm/drm_prime.c | 9 +++++++++ 3 files changed, 40 insertions(+), 9 deletions(-)
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h index 6aaba14f5972..e71f75a2ab57 100644 --- a/include/drm/drm_gem.h +++ b/include/drm/drm_gem.h @@ -150,6 +150,20 @@ struct drm_gem_object_funcs { */ void (*vunmap)(struct drm_gem_object *obj, void *vaddr);
/**
* @mmap:
*
* Handle mmap() of the gem object, setup vma accordingly.
*
* This callback is optional.
*
* The callback is used by by both drm_gem_mmap_obj() and
* drm_gem_prime_mmap(). When @mmap is present @vm_ops is not
* used, the @mmap callback must set vma->vm_ops instead.
*
*/
int (*mmap)(struct drm_gem_object *obj, struct vm_area_struct *vma);
/** * @vm_ops: *
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c index 6854f5867d51..aabde003ac4a 100644 --- a/drivers/gpu/drm/drm_gem.c +++ b/drivers/gpu/drm/drm_gem.c @@ -1099,22 +1099,30 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size, struct vm_area_struct *vma) { struct drm_device *dev = obj->dev;
int ret; /* Check for valid size. */ if (obj_size < vma->vm_end - vma->vm_start) return -EINVAL;
if (obj->funcs && obj->funcs->vm_ops)
vma->vm_ops = obj->funcs->vm_ops;
else if (dev->driver->gem_vm_ops)
vma->vm_ops = dev->driver->gem_vm_ops;
else
return -EINVAL;
if (obj->funcs && obj->funcs->mmap) {
ret = obj->funcs->mmap(obj, vma);
if (ret)
return ret;
} else {
if (obj->funcs && obj->funcs->vm_ops)
vma->vm_ops = obj->funcs->vm_ops;
else if (dev->driver->gem_vm_ops)
vma->vm_ops = dev->driver->gem_vm_ops;
else
return -EINVAL;
vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
}
Totally unrelated discussion around HMM lead me to a bit a chase, and realizing that we probably want a
WARN_ON(!(vma->vm_flags & VM_SPECIAL));
here, to make sure drivers set at least one of the "this is a special vma, don't try to treat it like pagecache/anon memory". Just to be on the safe side. Maybe we also want to keep the entire vma->vm_flags assignment in the common code, but at least the WARN_ON would be a good check I think. Maybe also check for VM_DONTEXPAND while at it (that would also break things badly if it's not set). VM_DONTDUMP I think is leftover from when drm drivers exposed register mmaps to userspace.
Anyway, just some detail questions, I think this looks real good.
Thanks, Daniel
vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP; vma->vm_private_data = obj;
vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot); /* Take a ref for this mapping of the object, so that the fault * handler can dereference the mmap offset's pointer to the object.
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 0a2316e0e812..0814211b0f3f 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -713,6 +713,15 @@ int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma) struct file *fil; int ret;
if (obj->funcs && obj->funcs->mmap) {
ret = obj->funcs->mmap(obj, vma);
if (ret)
return ret;
vma->vm_private_data = obj;
drm_gem_object_get(obj);
return 0;
}
priv = kzalloc(sizeof(*priv), GFP_KERNEL); fil = kzalloc(sizeof(*fil), GFP_KERNEL); if (!priv || !fil) {
-- 2.18.1
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-- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch