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Message-ID: <e091063c-2c4a-866e-acdb-9efb1e20d737@amd.com>
Date: Wed, 4 Dec 2019 12:11:23 +0100
From: Christian König <christian.koenig@....com>
To: Thomas Hellström (VMware)
<thomas_os@...pmail.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Cc: pv-drivers@...are.com, linux-graphics-maintainer@...are.com,
Thomas Hellstrom <thellstrom@...are.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...e.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Ralph Campbell <rcampbell@...dia.com>,
Jérôme Glisse <jglisse@...hat.com>
Subject: Re: [PATCH 6/8] drm: Add a drm_get_unmapped_area() helper
Am 03.12.19 um 14:22 schrieb Thomas Hellström (VMware):
> From: Thomas Hellstrom <thellstrom@...are.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@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: "Christian König" <christian.koenig@....com>
> Signed-off-by: Thomas Hellstrom <thellstrom@...are.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_ */
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