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Message-ID: <20251015153018.43735-4-loic.molinari@collabora.com>
Date: Wed, 15 Oct 2025 17:30:07 +0200
From: Loïc Molinari <loic.molinari@...labora.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>,
Simona Vetter <simona@...ll.ch>,
Jani Nikula <jani.nikula@...ux.intel.com>,
Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@...el.com>,
Tvrtko Ursulin <tursulin@...ulin.net>,
Boris Brezillon <boris.brezillon@...labora.com>,
Rob Herring <robh@...nel.org>,
Steven Price <steven.price@....com>,
Liviu Dudau <liviu.dudau@....com>,
Melissa Wen <mwen@...lia.com>,
Maíra Canal <mcanal@...lia.com>,
Hugh Dickins <hughd@...gle.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Loïc Molinari <loic.molinari@...labora.com>,
Al Viro <viro@...iv.linux.org.uk>,
Mikołaj Wasiak <mikolaj.wasiak@...el.com>,
Christian Brauner <brauner@...nel.org>,
Nitin Gote <nitin.r.gote@...el.com>,
Andi Shyti <andi.shyti@...ux.intel.com>,
Jonathan Corbet <corbet@....net>,
Christopher Healy <healych@...zon.com>,
Matthew Wilcox <willy@...radead.org>,
Bagas Sanjaya <bagasdotme@...il.com>
Cc: linux-kernel@...r.kernel.org,
dri-devel@...ts.freedesktop.org,
intel-gfx@...ts.freedesktop.org,
linux-mm@...ck.org,
linux-doc@...r.kernel.org,
kernel@...labora.com
Subject: [PATCH v4 03/13] drm/shmem-helper: Map huge pages in fault handlers
Check whether the starting address in the fault-around handler or the
faulty address in the fault handler is part of a huge page in order to
attempt a PMD sized PFN insertion into the VMA.
On builds with CONFIG_TRANSPARENT_HUGEPAGE enabled, if the mmap() user
address is PMD size aligned, if the GEM object is backed by shmem
buffers on mount points setting the 'huge=' option and if the shmem
backing store manages to allocate a huge folio, CPU mapping would then
benefit from significantly increased memcpy() performance. When these
conditions are met on a system with 2 MiB huge pages, an aligned copy
of 2 MiB would raise a single page fault instead of 4096.
v4:
- Implement map_pages instead of huge_fault
Signed-off-by: Loïc Molinari <loic.molinari@...labora.com>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 57 +++++++++++++++++++++-----
1 file changed, 46 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index e151262332f9..5d11bea573fe 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -580,6 +580,26 @@ static bool drm_gem_shmem_fault_is_valid(struct drm_gem_object *obj,
return true;
}
+static bool drm_gem_shmem_map_pmd(struct vm_fault *vmf, unsigned long addr,
+ struct page *page)
+{
+#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
+ unsigned long pfn = page_to_pfn(page);
+ unsigned long paddr = pfn << PAGE_SHIFT;
+ bool aligned = (addr & ~PMD_MASK) == (paddr & ~PMD_MASK);
+
+ if (aligned &&
+ pmd_none(*vmf->pmd) &&
+ folio_test_pmd_mappable(page_folio(page))) {
+ pfn &= PMD_MASK >> PAGE_SHIFT;
+ if (vmf_insert_pfn_pmd(vmf, pfn, false) == VM_FAULT_NOPAGE)
+ return true;
+ }
+#endif
+
+ return false;
+}
+
static vm_fault_t drm_gem_shmem_map_pages(struct vm_fault *vmf,
pgoff_t start_pgoff,
pgoff_t end_pgoff)
@@ -587,6 +607,7 @@ static vm_fault_t drm_gem_shmem_map_pages(struct vm_fault *vmf,
struct vm_area_struct *vma = vmf->vma;
struct drm_gem_object *obj = vma->vm_private_data;
struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+ struct page **pages = shmem->pages;
unsigned long addr, pfn;
vm_fault_t ret;
@@ -598,15 +619,22 @@ static vm_fault_t drm_gem_shmem_map_pages(struct vm_fault *vmf,
if (unlikely(!drm_gem_shmem_fault_is_valid(obj, start_pgoff))) {
ret = VM_FAULT_SIGBUS;
- } else {
- /* Map a range of pages around the faulty address. */
- do {
- pfn = page_to_pfn(shmem->pages[start_pgoff]);
- ret = vmf_insert_pfn(vma, addr, pfn);
- addr += PAGE_SIZE;
- } while (++start_pgoff <= end_pgoff && ret == VM_FAULT_NOPAGE);
+ goto out;
}
+ if (drm_gem_shmem_map_pmd(vmf, addr, pages[start_pgoff])) {
+ ret = VM_FAULT_NOPAGE;
+ goto out;
+ }
+
+ /* Map a range of pages around the faulty address. */
+ do {
+ pfn = page_to_pfn(pages[start_pgoff]);
+ ret = vmf_insert_pfn(vma, addr, pfn);
+ addr += PAGE_SIZE;
+ } while (++start_pgoff <= end_pgoff && ret == VM_FAULT_NOPAGE);
+
+ out:
dma_resv_unlock(shmem->base.resv);
return ret;
@@ -617,8 +645,9 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
struct vm_area_struct *vma = vmf->vma;
struct drm_gem_object *obj = vma->vm_private_data;
struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
- struct page *page;
+ struct page **pages = shmem->pages;
pgoff_t page_offset;
+ unsigned long pfn;
vm_fault_t ret;
/* Offset to faulty address in the VMA (without the fake offset). */
@@ -628,12 +657,18 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
if (unlikely(!drm_gem_shmem_fault_is_valid(obj, page_offset))) {
ret = VM_FAULT_SIGBUS;
- } else {
- page = shmem->pages[page_offset];
+ goto out;
+ }
- ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
+ if (drm_gem_shmem_map_pmd(vmf, vmf->address, pages[page_offset])) {
+ ret = VM_FAULT_NOPAGE;
+ goto out;
}
+ pfn = page_to_pfn(pages[page_offset]);
+ ret = vmf_insert_pfn(vma, vmf->address, pfn);
+
+ out:
dma_resv_unlock(shmem->base.resv);
return ret;
--
2.47.3
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