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Message-ID: <20251006085247.52f29f59@fedora>
Date: Mon, 6 Oct 2025 08:52:47 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Loïc Molinari <loic.molinari@...labora.com>
Cc: 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>, 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>,
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>,
Christopher Healy <healych@...zon.com>, linux-kernel@...r.kernel.org,
dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
linux-mm@...ck.org, kernel@...labora.com, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v3 01/10] drm/shmem-helper: Add huge page fault handler
On Sat, 4 Oct 2025 11:30:44 +0200
Loïc Molinari <loic.molinari@...labora.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@...labora.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
> Reported-by: kernel test robot <lkp@...el.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,
> };
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