Re: [PATCH] mm/dev_pfn: Exclude MEMORY_DEVICE_PRIVATE while computing virtual address

[Andrew Morton]

On Fri, 17 May 2019 16:08:34 +0530 Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote:

> The presence of struct page does not guarantee linear mapping for the pfn
> physical range. Device private memory which is non-coherent is excluded
> from linear mapping during devm_memremap_pages() though they will still
> have struct page coverage. Just check for device private memory before
> giving out virtual address for a given pfn.

I was going to give my standard "what are the user-visible runtime
effects of this change?", but...

> All these helper functions are all pfn_t related but could not figure out
> another way of determining a private pfn without looking into it's struct
> page. pfn_t_to_virt() is not getting used any where in mainline kernel.Is
> it used by out of tree drivers ? Should we then drop it completely ?

Yeah, let's kill it.

But first, let's fix it so that if someone brings it back, they bring
back a non-buggy version.

So...  what (would be) the user-visible runtime effects of this change?