This gives the mm subsystem the ability to propose the insertion of
PUD or PMD-sized mappings for the faulting addresses.
On builds with CONFIG_TRANSPARENT_HUGEPAGE enabled, if the mmap() user
address is aligned to a huge page size, 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, the CPU mapping
will 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.
v2:
- set ret to VM_FAULT_FALLBACK in default switch statement
- ifdef out paddr declaration
Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202509241315.8jjCyL7U-lkp@intel.com/
Closes: https://lore.kernel.org/oe-kbuild-all/202509241654.qJk1H5kr-lkp@intel.com/
Closes: https://lore.kernel.org/oe-kbuild-all/202509241920.PtSEkfd4-lkp@intel.com/
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 56 ++++++++++++++++++++++++--
1 file changed, 52 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..22c4b09e10a3 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 +583,10 @@ 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;
+#if defined(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP) || defined(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP)
+ unsigned long paddr;
+#endif
/* We don't use vmf->pgoff since that has the fake offset */
page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
@@ -592,17 +597,57 @@ 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;
+ }
- ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
+ 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
+
+ default:
+ ret = VM_FAULT_FALLBACK;
+ break;
}
+ 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 +684,9 @@ 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
Hi Loic,
...
> + unsigned int order)
> {
> struct vm_area_struct *vma = vmf->vma;
> struct drm_gem_object *obj = vma->vm_private_data;
> @@ -582,6 +583,10 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
> vm_fault_t ret;
we could initialize ret to VM_FAULT_FALLBACK and avoid the else's
and the default case.
> struct page *page;
> pgoff_t page_offset;
> + unsigned long pfn;
> +#if defined(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP) || defined(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP)
> + unsigned long paddr;
> +#endif
we could declare paddr inside the switch case in order to avoid
some extra ifdefs.
> /* We don't use vmf->pgoff since that has the fake offset */
> page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
> @@ -592,17 +597,57 @@ 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;
> + }
>
> - ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
> + page = shmem->pages[page_offset];
> + pfn = page_to_pfn(page);
> +
> + switch (order) {
> + case 0:
'0' needs to be defined, what does '0' mean? (I know what it
means, but for consistency I think it should have its own name).
Andi
> + ret = vmf_insert_pfn(vma, vmf->address, pfn);
> + break;
On Sat, 4 Oct 2025 11:30:44 +0200
Loïc Molinari <loic.molinari@collabora.com> wrote:
> This gives the mm subsystem the ability to propose the insertion of
> PUD or PMD-sized mappings for the faulting addresses.
>
> On builds with CONFIG_TRANSPARENT_HUGEPAGE enabled, if the mmap() user
> address is aligned to a huge page size, 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, the CPU mapping
> will 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.
>
> v2:
> - set ret to VM_FAULT_FALLBACK in default switch statement
> - ifdef out paddr declaration
>
> Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202509241315.8jjCyL7U-lkp@intel.com/
> Closes: https://lore.kernel.org/oe-kbuild-all/202509241654.qJk1H5kr-lkp@intel.com/
> Closes: https://lore.kernel.org/oe-kbuild-all/202509241920.PtSEkfd4-lkp@intel.com/
I'm not sure those Closes/Reported-by tags are needed when you fix bugs
introduced in a previous revisions of the patchset.
> ---
> drivers/gpu/drm/drm_gem_shmem_helper.c | 56 ++++++++++++++++++++++++--
> 1 file changed, 52 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..22c4b09e10a3 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 +583,10 @@ 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;
> +#if defined(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP) || defined(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP)
> + unsigned long paddr;
> +#endif
>
> /* We don't use vmf->pgoff since that has the fake offset */
> page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
> @@ -592,17 +597,57 @@ 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;
> + }
>
> - ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
> + 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
> +
> + default:
> + ret = VM_FAULT_FALLBACK;
> + break;
> }
>
> + 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 +684,9 @@ 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,
> };
On Sat, Oct 04, 2025 at 11:30:44AM +0200, Loïc Molinari wrote: > -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) From the mm side, we'd much rather you implemented ->map_pages than ->huge_fault. It's far more flexible; for example it'll support ARM's contpte which ->huge_fault() doesn't.
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