Re: [PATCH 6/8] drm: Add a drm_get_unmapped_area() helper
From: Christian KÃnig
Date: Wed Dec 04 2019 - 06:12:57 EST
Am 03.12.19 um 14:22 schrieb Thomas HellstrÃm (VMware):
From: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
Cc: "Christian KÃnig" <christian.koenig@xxxxxxx>
Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
---
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_ */