Re: [PATCH v2 2/6] drm/shmem_helper: use vmf_insert_pfn_mkwrite()

On Tue, Aug 4, 2026 at 4:42 PM Boris Brezillon
<[email protected]> wrote:
> Okay, I thought I'd ask to be sure, because of all the implementations
> of pfn_mkwrite listed here [1], only drm_gem_shmem_helper.c and
> kernel/events/core.c do that.

Also the vmwgfx one in patch 3; and for the !DAX case ext4 and XFS too
(e.g. xfs_filemap_pfn_mkwrite gets to iomap_page_mkwrite, not to
filemap_fault).

> The rest have their "generic" fault
> handler (by generic I mean a fault handler helper that covers all the
> order/WRITE_FLAG combinations) called from pfn_mkwrite(), and return a
> non-zero vm_fault_t.

I see; I think you can do that, it is handled at
https://elixir.bootlin.com/linux/v7.2-rc5/source/mm/memory.c#L2681 and
indeed it returns VM_FAULT_NOPAGE. But it's more or work for no real
reason. Your .pfn_mkwrite is a single line of code and it is clearer
IMO if you can see that try_insert_pfn() is calling the same helper as
.pfn_mkwrite().

Paolo