On Thu, Jul 22, 2021 at 08:50:48PM +0200, Thomas Zimmermann wrote:
> Hi
>
> Am 13.07.21 um 22:51 schrieb Daniel Vetter:
> > Aside from deleting lots of code the real motivation here is to switch
> > the mmap over to VM_PFNMAP, to be more consistent with what real gpu
> > drivers do. They're all VM_PFNMP, which means get_user_pages doesn't
> > work, and even if you try and there's a struct page behind that,
> > touching it and mucking around with its refcount can upset drivers
> > real bad.
> >
> > v2: Review from Thomas:
> > - sort #include
> > - drop more dead code that I didn't spot somehow
> >
> > v3: select DRM_GEM_SHMEM_HELPER to make it build (intel-gfx-ci)
> >
> > v4: I got tricked by 0cf2ef46c6c0 ("drm/shmem-helper: Use cached
> > mappings by default"), and we need WC in vgem because vgem doesn't
> > have explicit begin/end cpu access ioctls.
> >
> > Also add a comment why exactly vgem has to use wc.
> >
> > v5: Don't set obj->base.funcs, it will default to drm_gem_shmem_funcs
> > (Thomas)
> >
> > v6: vgem also needs an MMU for remapping
> >
> > Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > Cc: John Stultz <john.stultz@xxxxxxxxxx>
> > Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> > Cc: "Christian König" <christian.koenig@xxxxxxx>
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > Cc: Melissa Wen <melissa.srw@xxxxxxxxx>
> > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/Kconfig | 5 +-
> > drivers/gpu/drm/vgem/vgem_drv.c | 315 ++------------------------------
> > 2 files changed, 15 insertions(+), 305 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index 314eefa39892..28f7d2006e8b 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -272,7 +272,8 @@ source "drivers/gpu/drm/kmb/Kconfig"
> > config DRM_VGEM
> > tristate "Virtual GEM provider"
> > - depends on DRM
> > + depends on DRM && MMU
> > + select DRM_GEM_SHMEM_HELPER
> > help
> > Choose this option to get a virtual graphics memory manager,
> > as used by Mesa's software renderer for enhanced performance.
> > @@ -280,7 +281,7 @@ config DRM_VGEM
> > config DRM_VKMS
> > tristate "Virtual KMS (EXPERIMENTAL)"
> > - depends on DRM
> > + depends on DRM && MMU
> > select DRM_KMS_HELPER
> > select DRM_GEM_SHMEM_HELPER
> > select CRC32
> > diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
> > index bf38a7e319d1..ba410ba6b7f7 100644
> > --- a/drivers/gpu/drm/vgem/vgem_drv.c
> > +++ b/drivers/gpu/drm/vgem/vgem_drv.c
> > @@ -38,6 +38,7 @@
> > #include <drm/drm_drv.h>
> > #include <drm/drm_file.h>
> > +#include <drm/drm_gem_shmem_helper.h>
> > #include <drm/drm_ioctl.h>
> > #include <drm/drm_managed.h>
> > #include <drm/drm_prime.h>
> > @@ -50,87 +51,11 @@
> > #define DRIVER_MAJOR 1
> > #define DRIVER_MINOR 0
> > -static const struct drm_gem_object_funcs vgem_gem_object_funcs;
> > -
> > static struct vgem_device {
> > struct drm_device drm;
> > struct platform_device *platform;
> > } *vgem_device;
> > -static void vgem_gem_free_object(struct drm_gem_object *obj)
> > -{
> > - struct drm_vgem_gem_object *vgem_obj = to_vgem_bo(obj);
> > -
> > - kvfree(vgem_obj->pages);
> > - mutex_destroy(&vgem_obj->pages_lock);
> > -
> > - if (obj->import_attach)
> > - drm_prime_gem_destroy(obj, vgem_obj->table);
> > -
> > - drm_gem_object_release(obj);
> > - kfree(vgem_obj);
> > -}
> > -
> > -static vm_fault_t vgem_gem_fault(struct vm_fault *vmf)
> > -{
> > - struct vm_area_struct *vma = vmf->vma;
> > - struct drm_vgem_gem_object *obj = vma->vm_private_data;
> > - /* We don't use vmf->pgoff since that has the fake offset */
> > - unsigned long vaddr = vmf->address;
> > - vm_fault_t ret = VM_FAULT_SIGBUS;
> > - loff_t num_pages;
> > - pgoff_t page_offset;
> > - page_offset = (vaddr - vma->vm_start) >> PAGE_SHIFT;
> > -
> > - num_pages = DIV_ROUND_UP(obj->base.size, PAGE_SIZE);
> > -
> > - if (page_offset >= num_pages)
> > - return VM_FAULT_SIGBUS;
> > -
> > - mutex_lock(&obj->pages_lock);
> > - if (obj->pages) {
> > - get_page(obj->pages[page_offset]);
> > - vmf->page = obj->pages[page_offset];
> > - ret = 0;
> > - }
> > - mutex_unlock(&obj->pages_lock);
> > - if (ret) {
> > - struct page *page;
> > -
> > - page = shmem_read_mapping_page(
> > - file_inode(obj->base.filp)->i_mapping,
> > - page_offset);
> > - if (!IS_ERR(page)) {
> > - vmf->page = page;
> > - ret = 0;
> > - } else switch (PTR_ERR(page)) {
> > - case -ENOSPC:
> > - case -ENOMEM:
> > - ret = VM_FAULT_OOM;
> > - break;
> > - case -EBUSY:
> > - ret = VM_FAULT_RETRY;
> > - break;
> > - case -EFAULT:
> > - case -EINVAL:
> > - ret = VM_FAULT_SIGBUS;
> > - break;
> > - default:
> > - WARN_ON(PTR_ERR(page));
> > - ret = VM_FAULT_SIGBUS;
> > - break;
> > - }
> > -
> > - }
> > - return ret;
> > -}
> > -
> > -static const struct vm_operations_struct vgem_gem_vm_ops = {
> > - .fault = vgem_gem_fault,
> > - .open = drm_gem_vm_open,
> > - .close = drm_gem_vm_close,
> > -};
> > -
> > static int vgem_open(struct drm_device *dev, struct drm_file *file)
> > {
> > struct vgem_file *vfile;
> > @@ -159,81 +84,6 @@ static void vgem_postclose(struct drm_device *dev, struct drm_file *file)
> > kfree(vfile);
> > }
> > -static struct drm_vgem_gem_object *__vgem_gem_create(struct drm_device *dev,
> > - unsigned long size)
> > -{
> > - struct drm_vgem_gem_object *obj;
> > - int ret;
> > -
> > - obj = kzalloc(sizeof(*obj), GFP_KERNEL);
> > - if (!obj)
> > - return ERR_PTR(-ENOMEM);
> > -
> > - obj->base.funcs = &vgem_gem_object_funcs;
> > -
> > - ret = drm_gem_object_init(dev, &obj->base, roundup(size, PAGE_SIZE));
> > - if (ret) {
> > - kfree(obj);
> > - return ERR_PTR(ret);
> > - }
> > -
> > - mutex_init(&obj->pages_lock);
> > -
> > - return obj;
> > -}
> > -
> > -static void __vgem_gem_destroy(struct drm_vgem_gem_object *obj)
> > -{
> > - drm_gem_object_release(&obj->base);
> > - kfree(obj);
> > -}
> > -
> > -static struct drm_gem_object *vgem_gem_create(struct drm_device *dev,
> > - struct drm_file *file,
> > - unsigned int *handle,
> > - unsigned long size)
> > -{
> > - struct drm_vgem_gem_object *obj;
> > - int ret;
> > -
> > - obj = __vgem_gem_create(dev, size);
> > - if (IS_ERR(obj))
> > - return ERR_CAST(obj);
> > -
> > - ret = drm_gem_handle_create(file, &obj->base, handle);
> > - if (ret) {
> > - drm_gem_object_put(&obj->base);
> > - return ERR_PTR(ret);
> > - }
> > -
> > - return &obj->base;
> > -}
> > -
> > -static int vgem_gem_dumb_create(struct drm_file *file, struct drm_device *dev,
> > - struct drm_mode_create_dumb *args)
> > -{
> > - struct drm_gem_object *gem_object;
> > - u64 pitch, size;
> > -
> > - pitch = args->width * DIV_ROUND_UP(args->bpp, 8);
> > - size = args->height * pitch;
> > - if (size == 0)
> > - return -EINVAL;
> > -
> > - gem_object = vgem_gem_create(dev, file, &args->handle, size);
> > - if (IS_ERR(gem_object))
> > - return PTR_ERR(gem_object);
> > -
> > - args->size = gem_object->size;
> > - args->pitch = pitch;
> > -
> > - drm_gem_object_put(gem_object);
> > -
> > - DRM_DEBUG("Created object of size %llu\n", args->size);
> > -
> > - return 0;
> > -}
> > -
> > static struct drm_ioctl_desc vgem_ioctls[] = {
> > DRM_IOCTL_DEF_DRV(VGEM_FENCE_ATTACH, vgem_fence_attach_ioctl, DRM_RENDER_ALLOW),
> > DRM_IOCTL_DEF_DRV(VGEM_FENCE_SIGNAL, vgem_fence_signal_ioctl, DRM_RENDER_ALLOW),
> > @@ -266,159 +116,23 @@ static const struct file_operations vgem_driver_fops = {
> > .release = drm_release,
> > };
> > -static struct page **vgem_pin_pages(struct drm_vgem_gem_object *bo)
> > -{
> > - mutex_lock(&bo->pages_lock);
> > - if (bo->pages_pin_count++ == 0) {
> > - struct page **pages;
> > -
> > - pages = drm_gem_get_pages(&bo->base);
> > - if (IS_ERR(pages)) {
> > - bo->pages_pin_count--;
> > - mutex_unlock(&bo->pages_lock);
> > - return pages;
> > - }
> > -
> > - bo->pages = pages;
> > - }
> > - mutex_unlock(&bo->pages_lock);
> > -
> > - return bo->pages;
> > -}
> > -
> > -static void vgem_unpin_pages(struct drm_vgem_gem_object *bo)
> > +static struct drm_gem_object *vgem_gem_create_object(struct drm_device *dev, size_t size)
> > {
> > - mutex_lock(&bo->pages_lock);
> > - if (--bo->pages_pin_count == 0) {
> > - drm_gem_put_pages(&bo->base, bo->pages, true, true);
> > - bo->pages = NULL;
> > - }
> > - mutex_unlock(&bo->pages_lock);
> > -}
> > + struct drm_gem_shmem_object *obj;
> > -static int vgem_prime_pin(struct drm_gem_object *obj)
> > -{
> > - struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
> > - long n_pages = obj->size >> PAGE_SHIFT;
> > - struct page **pages;
> > -
> > - pages = vgem_pin_pages(bo);
> > - if (IS_ERR(pages))
> > - return PTR_ERR(pages);
> > + obj = kzalloc(sizeof(*obj), GFP_KERNEL);
> > + if (!obj)
> > + return NULL;
> > - /* Flush the object from the CPU cache so that importers can rely
> > - * on coherent indirect access via the exported dma-address.
> > + /*
> > + * vgem doesn't have any begin/end cpu access ioctls, therefore must use
> > + * coherent memory or dma-buf sharing just wont work.
> > */
> > - drm_clflush_pages(pages, n_pages);
>
> Instead of shoehorning GEM SHMEM to get caching right (patch 2) have you
> considered to set your own GEM funcs object for vgem. All function pointers
> would point to SHMEM functions, except for pin, which would be
> drm_gem_shmem_pin() + drm_clflush_pages(). If this works, I think it would
> be much preferable to the current patch 2. You can override the default GEM
> functions from within vgem_gem_create_object().
The thing is: shmem helpers currently get the caching wrong for wc. vgem
is just the messenger.
Also, get_pages + drm_clflush is not actually guaranteed to be enough
across platforms. It is enough on intel x86 cpus (and I think all modern
amd x86 cpus, but not some earlier ones from way back), but not in general
across the board.
-Daniel
>
> Best regards
> Thomas
>
>
> > -
> > - return 0;
> > -}
> > -
> > -static void vgem_prime_unpin(struct drm_gem_object *obj)
> > -{
> > - struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
> > -
> > - vgem_unpin_pages(bo);
> > -}
> > -
> > -static struct sg_table *vgem_prime_get_sg_table(struct drm_gem_object *obj)
> > -{
> > - struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
> > -
> > - return drm_prime_pages_to_sg(obj->dev, bo->pages, bo->base.size >> PAGE_SHIFT);
> > -}
> > -
> > -static struct drm_gem_object* vgem_prime_import(struct drm_device *dev,
> > - struct dma_buf *dma_buf)
> > -{
> > - struct vgem_device *vgem = container_of(dev, typeof(*vgem), drm);
> > -
> > - return drm_gem_prime_import_dev(dev, dma_buf, &vgem->platform->dev);
> > -}
> > -
> > -static struct drm_gem_object *vgem_prime_import_sg_table(struct drm_device *dev,
> > - struct dma_buf_attachment *attach, struct sg_table *sg)
> > -{
> > - struct drm_vgem_gem_object *obj;
> > - int npages;
> > -
> > - obj = __vgem_gem_create(dev, attach->dmabuf->size);
> > - if (IS_ERR(obj))
> > - return ERR_CAST(obj);
> > -
> > - npages = PAGE_ALIGN(attach->dmabuf->size) / PAGE_SIZE;
> > -
> > - obj->table = sg;
> > - obj->pages = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
> > - if (!obj->pages) {
> > - __vgem_gem_destroy(obj);
> > - return ERR_PTR(-ENOMEM);
> > - }
> > + obj->map_wc = true;
> > - obj->pages_pin_count++; /* perma-pinned */
> > - drm_prime_sg_to_page_array(obj->table, obj->pages, npages);
> > return &obj->base;
> > }
> > -static int vgem_prime_vmap(struct drm_gem_object *obj, struct dma_buf_map *map)
> > -{
> > - struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
> > - long n_pages = obj->size >> PAGE_SHIFT;
> > - struct page **pages;
> > - void *vaddr;
> > -
> > - pages = vgem_pin_pages(bo);
> > - if (IS_ERR(pages))
> > - return PTR_ERR(pages);
> > -
> > - vaddr = vmap(pages, n_pages, 0, pgprot_writecombine(PAGE_KERNEL));
> > - if (!vaddr)
> > - return -ENOMEM;
> > - dma_buf_map_set_vaddr(map, vaddr);
> > -
> > - return 0;
> > -}
> > -
> > -static void vgem_prime_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map)
> > -{
> > - struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
> > -
> > - vunmap(map->vaddr);
> > - vgem_unpin_pages(bo);
> > -}
> > -
> > -static int vgem_prime_mmap(struct drm_gem_object *obj,
> > - struct vm_area_struct *vma)
> > -{
> > - int ret;
> > -
> > - if (obj->size < vma->vm_end - vma->vm_start)
> > - return -EINVAL;
> > -
> > - if (!obj->filp)
> > - return -ENODEV;
> > -
> > - ret = call_mmap(obj->filp, vma);
> > - if (ret)
> > - return ret;
> > -
> > - vma_set_file(vma, obj->filp);
> > - vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
> > - vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
> > -
> > - return 0;
> > -}
> > -
> > -static const struct drm_gem_object_funcs vgem_gem_object_funcs = {
> > - .free = vgem_gem_free_object,
> > - .pin = vgem_prime_pin,
> > - .unpin = vgem_prime_unpin,
> > - .get_sg_table = vgem_prime_get_sg_table,
> > - .vmap = vgem_prime_vmap,
> > - .vunmap = vgem_prime_vunmap,
> > - .vm_ops = &vgem_gem_vm_ops,
> > -};
> > -
> > static const struct drm_driver vgem_driver = {
> > .driver_features = DRIVER_GEM | DRIVER_RENDER,
> > .open = vgem_open,
> > @@ -427,13 +141,8 @@ static const struct drm_driver vgem_driver = {
> > .num_ioctls = ARRAY_SIZE(vgem_ioctls),
> > .fops = &vgem_driver_fops,
> > - .dumb_create = vgem_gem_dumb_create,
> > -
> > - .prime_handle_to_fd = drm_gem_prime_handle_to_fd,
> > - .prime_fd_to_handle = drm_gem_prime_fd_to_handle,
> > - .gem_prime_import = vgem_prime_import,
> > - .gem_prime_import_sg_table = vgem_prime_import_sg_table,
> > - .gem_prime_mmap = vgem_prime_mmap,
> > + DRM_GEM_SHMEM_DRIVER_OPS,
> > + .gem_create_object = vgem_gem_create_object,
> > .name = DRIVER_NAME,
> > .desc = DRIVER_DESC,
> >
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
