linux-kernel - Re: [PATCH v3 01/10] drm/shmem-helper: Add huge page fault handler

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Message-ID: <fbfii7x7ypvbsowp63zuayzykqmpjpdjvzjdpyswwhfttuwemd@wbs7qxp5zie6>
Date: Mon, 6 Oct 2025 18:01:53 +0200
From: Andi Shyti <andi.shyti@...nel.org>
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>, 
	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>, 
	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

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;