Re: [PATCH 6/8] drm: Add a drm_get_unmapped_area() helper

["Christian König" <christian.koenig@amd.com>]

Am 03.12.19 um 14:22 schrieb Thomas Hellström (VMware):
> From: Thomas Hellstrom <thellstrom@vmware.com>
>
> This helper is used to align user-space buffer object addresses to
> huge page boundaries, minimizing the chance of alignment mismatch
> between user-space addresses and physical addresses.

Mhm, I'm wondering if that is really such a good idea.

Wouldn't it be sufficient if userspace uses MAP_HUGETLB?

Regards,
Christian.

>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Cc: Ralph Campbell <rcampbell@nvidia.com>
> Cc: "Jérôme Glisse" <jglisse@redhat.com>
> Cc: "Christian König" <christian.koenig@amd.com>
> Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
> ---
>   drivers/gpu/drm/drm_file.c | 130 +++++++++++++++++++++++++++++++++++++
>   include/drm/drm_file.h     |   5 ++
>   2 files changed, 135 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index ea34bc991858..e5b4024cd397 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -31,6 +31,8 @@
>    * OTHER DEALINGS IN THE SOFTWARE.
>    */
>   
> +#include <uapi/asm/mman.h>
> +
>   #include <linux/dma-fence.h>
>   #include <linux/module.h>
>   #include <linux/pci.h>
> @@ -41,6 +43,7 @@
>   #include <drm/drm_drv.h>
>   #include <drm/drm_file.h>
>   #include <drm/drm_print.h>
> +#include <drm/drm_vma_manager.h>
>   
>   #include "drm_crtc_internal.h"
>   #include "drm_internal.h"
> @@ -754,3 +757,130 @@ void drm_send_event(struct drm_device *dev, struct drm_pending_event *e)
>   	spin_unlock_irqrestore(&dev->event_lock, irqflags);
>   }
>   EXPORT_SYMBOL(drm_send_event);
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +/*
> + * drm_addr_inflate() attempts to construct an aligned area by inflating
> + * the area size and skipping the unaligned start of the area.
> + * adapted from shmem_get_unmapped_area()
> + */
> +static unsigned long drm_addr_inflate(unsigned long addr,
> +				      unsigned long len,
> +				      unsigned long pgoff,
> +				      unsigned long flags,
> +				      unsigned long huge_size)
> +{
> +	unsigned long offset, inflated_len;
> +	unsigned long inflated_addr;
> +	unsigned long inflated_offset;
> +
> +	offset = (pgoff << PAGE_SHIFT) & (huge_size - 1);
> +	if (offset && offset + len < 2 * huge_size)
> +		return addr;
> +	if ((addr & (huge_size - 1)) == offset)
> +		return addr;
> +
> +	inflated_len = len + huge_size - PAGE_SIZE;
> +	if (inflated_len > TASK_SIZE)
> +		return addr;
> +	if (inflated_len < len)
> +		return addr;
> +
> +	inflated_addr = current->mm->get_unmapped_area(NULL, 0, inflated_len,
> +						       0, flags);
> +	if (IS_ERR_VALUE(inflated_addr))
> +		return addr;
> +	if (inflated_addr & ~PAGE_MASK)
> +		return addr;
> +
> +	inflated_offset = inflated_addr & (huge_size - 1);
> +	inflated_addr += offset - inflated_offset;
> +	if (inflated_offset > offset)
> +		inflated_addr += huge_size;
> +
> +	if (inflated_addr > TASK_SIZE - len)
> +		return addr;
> +
> +	return inflated_addr;
> +}
> +
> +/**
> + * drm_get_unmapped_area() - Get an unused user-space virtual memory area
> + * suitable for huge page table entries.
> + * @file: The struct file representing the address space being mmap()'d.
> + * @uaddr: Start address suggested by user-space.
> + * @len: Length of the area.
> + * @pgoff: The page offset into the address space.
> + * @flags: mmap flags
> + * @mgr: The address space manager used by the drm driver. This argument can
> + * probably be removed at some point when all drivers use the same
> + * address space manager.
> + *
> + * This function attempts to find an unused user-space virtual memory area
> + * that can accommodate the size we want to map, and that is properly
> + * aligned to facilitate huge page table entries matching actual
> + * huge pages or huge page aligned memory in buffer objects. Buffer objects
> + * are assumed to start at huge page boundary pfns (io memory) or be
> + * populated by huge pages aligned to the start of the buffer object
> + * (system- or coherent memory). Adapted from shmem_get_unmapped_area.
> + *
> + * Return: aligned user-space address.
> + */
> +unsigned long drm_get_unmapped_area(struct file *file,
> +				    unsigned long uaddr, unsigned long len,
> +				    unsigned long pgoff, unsigned long flags,
> +				    struct drm_vma_offset_manager *mgr)
> +{
> +	unsigned long addr;
> +	unsigned long inflated_addr;
> +	struct drm_vma_offset_node *node;
> +
> +	if (len > TASK_SIZE)
> +		return -ENOMEM;
> +
> +	/* Adjust mapping offset to be zero at bo start */
> +	drm_vma_offset_lock_lookup(mgr);
> +	node = drm_vma_offset_lookup_locked(mgr, pgoff, 1);
> +	if (node)
> +		pgoff -= node->vm_node.start;
> +	drm_vma_offset_unlock_lookup(mgr);
> +
> +	addr = current->mm->get_unmapped_area(file, uaddr, len, pgoff, flags);
> +	if (IS_ERR_VALUE(addr))
> +		return addr;
> +	if (addr & ~PAGE_MASK)
> +		return addr;
> +	if (addr > TASK_SIZE - len)
> +		return addr;
> +
> +	if (len < HPAGE_PMD_SIZE)
> +		return addr;
> +	if (flags & MAP_FIXED)
> +		return addr;
> +	/*
> +	 * Our priority is to support MAP_SHARED mapped hugely;
> +	 * and support MAP_PRIVATE mapped hugely too, until it is COWed.
> +	 * But if caller specified an address hint, respect that as before.
> +	 */
> +	if (uaddr)
> +		return addr;
> +
> +	inflated_addr = drm_addr_inflate(addr, len, pgoff, flags,
> +					 HPAGE_PMD_SIZE);
> +
> +	if (IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
> +	    len >= HPAGE_PUD_SIZE)
> +		inflated_addr = drm_addr_inflate(inflated_addr, len, pgoff,
> +						 flags, HPAGE_PUD_SIZE);
> +	return inflated_addr;
> +}
> +#else /* CONFIG_TRANSPARENT_HUGEPAGE */
> +unsigned long drm_get_unmapped_area(struct file *file,
> +				    unsigned long uaddr, unsigned long len,
> +				    unsigned long pgoff, unsigned long flags,
> +				    struct drm_vma_offset_manager *mgr)
> +{
> +	return current->mm->get_unmapped_area(file, uaddr, len, pgoff, flags);
> +}
> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> +EXPORT_SYMBOL_GPL(drm_get_unmapped_area);
> diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
> index 67af60bb527a..4719cc80d547 100644
> --- a/include/drm/drm_file.h
> +++ b/include/drm/drm_file.h
> @@ -386,5 +386,10 @@ void drm_event_cancel_free(struct drm_device *dev,
>   			   struct drm_pending_event *p);
>   void drm_send_event_locked(struct drm_device *dev, struct drm_pending_event *e);
>   void drm_send_event(struct drm_device *dev, struct drm_pending_event *e);
> +struct drm_vma_offset_manager;
> +unsigned long drm_get_unmapped_area(struct file *file,
> +				    unsigned long uaddr, unsigned long len,
> +				    unsigned long pgoff, unsigned long flags,
> +				    struct drm_vma_offset_manager *mgr);
>   
>   #endif /* _DRM_FILE_H_ */