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* [PATCH] drm/shmem-helper: Add huge page fault handler
@ 2025-09-23  9:56 Loïc Molinari
  2025-09-24  6:23 ` kernel test robot
                   ` (3 more replies)
  0 siblings, 4 replies; 5+ messages in thread
From: Loïc Molinari @ 2025-09-23  9:56 UTC (permalink / raw)
  To: dri-devel
  Cc: kernel, Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann,
	David Airlie, Simona Vetter, Loïc Molinari

This gives the mm subsystem the ability to propose the insertion of a
PMD or PUD mapping for the faulting address.

If the virtual address provided from userspace with mmap() using the
address hint parameter is aligned to a huge page size, if the GEM
object is backed by a tmpfs mount point using Transparent Hugepage and
if the shmem backing store manages to allocate enough contiguous
physical pages to fit within a huge page, the CPU mapping will then
benefit from significantly increased memcpy() performance. For
instance, when these conditions are met on a system with 2 MiB huge
pages, a (fresh) aligned copy of 2 MiB would raise a single page fault
instead of 4096.

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 51 ++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 50594cf8e17c..30aa0d72093b 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -573,7 +573,8 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create);
 
-static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
+static vm_fault_t drm_gem_shmem_huge_fault(struct vm_fault *vmf,
+					   unsigned int order)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	struct drm_gem_object *obj = vma->vm_private_data;
@@ -582,6 +583,7 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
 	vm_fault_t ret;
 	struct page *page;
 	pgoff_t page_offset;
+	unsigned long pfn, paddr;
 
 	/* We don't use vmf->pgoff since that has the fake offset */
 	page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
@@ -592,17 +594,55 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
 	    drm_WARN_ON_ONCE(obj->dev, !shmem->pages) ||
 	    shmem->madv < 0) {
 		ret = VM_FAULT_SIGBUS;
-	} else {
-		page = shmem->pages[page_offset];
+		goto out;
+	}
+
+	page = shmem->pages[page_offset];
+	pfn = page_to_pfn(page);
+
+	switch (order) {
+	case 0:
+		ret = vmf_insert_pfn(vma, vmf->address, pfn);
+		break;
+
+#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
+	case PMD_ORDER:
+		paddr = pfn << PAGE_SHIFT;
+		if (((vmf->address & ~PMD_MASK) == (paddr & ~PMD_MASK)) &&
+		    (folio_order(page_folio(page)) == PMD_ORDER))
+			ret = vmf_insert_pfn_pmd(
+				    vmf, pfn & (PMD_MASK >> PAGE_SHIFT), false);
+		else
+			ret = VM_FAULT_FALLBACK;
+		break;
+#endif
+
+#ifdef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP
+	case PUD_ORDER:
+		paddr = pfn << PAGE_SHIFT;
+		if (((vmf->address & ~PUD_MASK) == (paddr & ~PUD_MASK)) &&
+		    (folio_order(page_folio(page)) == PUD_ORDER))
+			ret = vmf_insert_pfn_pud(
+				    vmf, pfn & (PUD_MASK >> PAGE_SHIFT), false);
+		else
+			ret = VM_FAULT_FALLBACK;
+		break;
+#endif
 
-		ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
+	default:
 	}
 
+ out:
 	dma_resv_unlock(shmem->base.resv);
 
 	return ret;
 }
 
+static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
+{
+	return drm_gem_shmem_huge_fault(vmf, 0);
+}
+
 static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
 {
 	struct drm_gem_object *obj = vma->vm_private_data;
@@ -639,6 +679,9 @@ static void drm_gem_shmem_vm_close(struct vm_area_struct *vma)
 
 const struct vm_operations_struct drm_gem_shmem_vm_ops = {
 	.fault = drm_gem_shmem_fault,
+#if defined(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP) || defined(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP)
+	.huge_fault = drm_gem_shmem_huge_fault,
+#endif
 	.open = drm_gem_shmem_vm_open,
 	.close = drm_gem_shmem_vm_close,
 };
-- 
2.47.3


^ permalink raw reply related	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2025-09-26  9:27 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-09-23  9:56 [PATCH] drm/shmem-helper: Add huge page fault handler Loïc Molinari
2025-09-24  6:23 ` kernel test robot
2025-09-24  8:45 ` kernel test robot
2025-09-24 12:04 ` kernel test robot
2025-09-26  9:26 ` Boris Brezillon

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