linux-kernel - Re: [PATCH] mm: Remove broken pfn_to_virt() on arch csky/hexagon/openrisc

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Date: Fri, 2 Feb 2024 18:43:00 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: arnd@...db.de, guoren@...nel.org, bcain@...cinc.com, jonas@...thpole.se, 
	stefan.kristiansson@...nalahti.fi, shorne@...il.com, 
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org, 
	linux-openrisc@...r.kernel.org
Subject: Re: [PATCH] mm: Remove broken pfn_to_virt() on arch csky/hexagon/openrisc

On Fri, Feb 2, 2024 at 3:35 PM Yan Zhao <yan.y.zhao@...el.com> wrote:

> Remove the broken pfn_to_virt() on architectures csky/hexagon/openrisc.
>
> The pfn_to_virt() on those architectures takes PFN instead of PA as the
> input to macro __va(), with PAGE_SHIFT applying to the converted VA, which
> is not right, especially when there's a non-zero offset in __va(). [1]
>
> The broken pfn_to_virt() was noticed when checking how page_to_virt() is
> unfolded on x86. It turns out that the one in linux/mm.h instead of in
> asm-generic/page.h is compiled for x86. However, page_to_virt() in
> asm-generic/page.h is found out expanding to pfn_to_virt() with a bug
> described above. The pfn_to_virt() is found out not right as well on
> architectures csky/hexagon/openrisc.
>
> Since there's no single caller on csky/hexagon/openrisc to pfn_to_virt()
> and there are functions doing similar things as pfn_to_virt() --
> - pfn_to_kaddr() in asm/page.h for csky,
> - page_to_virt() in asm/page.h for hexagon, and
> - page_to_virt() in linux/mm.h for openrisc,
> just delete the pfn_to_virt() on those architectures.
>
> The pfn_to_virt() in asm-generic/page.h is not touched in this patch as
> it's referenced by page_to_virt() in that header while the whole header is
> going to be removed as a whole due to no one including it.
>
> Link:https://lore.kernel.org/all/20240131055159.2506-1-yan.y.zhao@intel.com [1]
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>

Thanks for making the kernel a better place!
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij