Re: [PATCH] drm/shmem-helper: Switch to vmf_insert_pfn

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Jun 03, 2021 at 11:08:31PM +0200, Daniel Vetter wrote:
> We want to stop gup, which isn't the case if we use vmf_insert_page
> and VM_MIXEDMAP, because that does not set pte_special.
> 
> v2: With this shmem gem helpers now definitely need CONFIG_MMU (0day)
> 
> v3: add more depends on MMU. For usb drivers this is a bit awkward,
> but really it's correct: To be able to provide a contig mapping of
> buffers to userspace on !MMU platforms we'd need to use the cma
> helpers for these drivers on those platforms. As-is this wont work.
> 
> Also not exactly sure why vm_insert_page doesn't go boom, because that
> definitely wont fly in practice since the pages are non-contig to
> begin with.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>

Merged to drm-misc-next.

Aside, anyone feel like a review on the previous patch? Still not ready to
switch vgem over, but I think I've found the next bug that needs fixing in
shmem helpers.
-Daniel

> ---
>  drivers/gpu/drm/Kconfig                | 2 +-
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 4 ++--
>  drivers/gpu/drm/gud/Kconfig            | 2 +-
>  drivers/gpu/drm/tiny/Kconfig           | 4 ++--
>  drivers/gpu/drm/udl/Kconfig            | 1 +
>  5 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 56a55a6e6239..9c21527b791f 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -206,7 +206,7 @@ config DRM_KMS_CMA_HELPER
>  
>  config DRM_GEM_SHMEM_HELPER
>  	bool
> -	depends on DRM
> +	depends on DRM && MMU
>  	help
>  	  Choose this if you need the GEM shmem helper functions
>  
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 6d625cee7a6a..11edd54f0580 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -542,7 +542,7 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
>  	} else {
>  		page = shmem->pages[page_offset];
>  
> -		ret = vmf_insert_page(vma, vmf->address, page);
> +		ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
>  	}
>  
>  	mutex_unlock(&shmem->pages_lock);
> @@ -612,7 +612,7 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
>  		return ret;
>  	}
>  
> -	vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;
> +	vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND;
>  	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>  	if (shmem->map_wc)
>  		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> diff --git a/drivers/gpu/drm/gud/Kconfig b/drivers/gpu/drm/gud/Kconfig
> index 1c8601bf4d91..9c1e61f9eec3 100644
> --- a/drivers/gpu/drm/gud/Kconfig
> +++ b/drivers/gpu/drm/gud/Kconfig
> @@ -2,7 +2,7 @@
>  
>  config DRM_GUD
>  	tristate "GUD USB Display"
> -	depends on DRM && USB
> +	depends on DRM && USB && MMU
>  	select LZ4_COMPRESS
>  	select DRM_KMS_HELPER
>  	select DRM_GEM_SHMEM_HELPER
> diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
> index d46f95d9196d..a15f57ace9e7 100644
> --- a/drivers/gpu/drm/tiny/Kconfig
> +++ b/drivers/gpu/drm/tiny/Kconfig
> @@ -31,7 +31,7 @@ config DRM_CIRRUS_QEMU
>  
>  config DRM_GM12U320
>  	tristate "GM12U320 driver for USB projectors"
> -	depends on DRM && USB
> +	depends on DRM && USB && MMU
>  	select DRM_KMS_HELPER
>  	select DRM_GEM_SHMEM_HELPER
>  	help
> @@ -40,7 +40,7 @@ config DRM_GM12U320
>  
>  config DRM_SIMPLEDRM
>  	tristate "Simple framebuffer driver"
> -	depends on DRM
> +	depends on DRM && MMU
>  	select DRM_GEM_SHMEM_HELPER
>  	select DRM_KMS_HELPER
>  	help
> diff --git a/drivers/gpu/drm/udl/Kconfig b/drivers/gpu/drm/udl/Kconfig
> index 1f497d8f1ae5..c744175c6992 100644
> --- a/drivers/gpu/drm/udl/Kconfig
> +++ b/drivers/gpu/drm/udl/Kconfig
> @@ -4,6 +4,7 @@ config DRM_UDL
>  	depends on DRM
>  	depends on USB
>  	depends on USB_ARCH_HAS_HCD
> +	depends on MMU
>  	select DRM_GEM_SHMEM_HELPER
>  	select DRM_KMS_HELPER
>  	help
> -- 
> 2.31.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch