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drm/shmem-helper: Map huge pages in fault handler

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Attempt a PMD sized PFN insertion into the VMA if the faulty address
of the fault handler is part of a huge page.

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 mountpoints 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

v6:
- get rid of map_pages handler for now (keep it for another series
  along with arm64 contpte support)

v11:
- remove page fault validity check helper
- rename drm_gem_shmem_map_pmd() to drm_gem_shmem_try_map_pmd()
- add Boris R-b

v12:
- move up ret var decl in fault handler to minimize diff

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patch.msgid.link/20251205182231.194072-3-loic.molinari@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
This commit is contained in:
Loïc Molinari 2025-12-05 19:22:23 +01:00 committed by Boris Brezillon
parent 9d2d49027c
commit 211b9a39f2
1 changed files with 32 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
drivers/gpu/drm/drm_gem_shmem_helper.c
View File

@ -567,6 +567,26 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
} }
EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create); EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create);
static bool drm_gem_shmem_try_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_fault(struct vm_fault *vmf) static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
{ {
struct vm_area_struct *vma = vmf->vma; struct vm_area_struct *vma = vmf->vma;
@ -574,8 +594,9 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj); struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
loff_t num_pages = obj->size >> PAGE_SHIFT; loff_t num_pages = obj->size >> PAGE_SHIFT;
vm_fault_t ret; vm_fault_t ret;
struct page *page; struct page **pages = shmem->pages;
pgoff_t page_offset; pgoff_t page_offset;
unsigned long pfn;
/* Offset to faulty address in the VMA. */ /* Offset to faulty address in the VMA. */
page_offset = vmf->pgoff - vma->vm_pgoff; page_offset = vmf->pgoff - vma->vm_pgoff;
@ -586,12 +607,18 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
drm_WARN_ON_ONCE(obj->dev, !shmem->pages) || drm_WARN_ON_ONCE(obj->dev, !shmem->pages) ||
shmem->madv < 0) { shmem->madv < 0) {
ret = VM_FAULT_SIGBUS; ret = VM_FAULT_SIGBUS;
} else { goto out;
page = shmem->pages[page_offset];
ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
} }
if (drm_gem_shmem_try_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); dma_resv_unlock(shmem->base.resv);
return ret; return ret;