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References: <20240202140550.9886-1-yan.y.zhao@intel.com>
In-Reply-To: <20240202140550.9886-1-yan.y.zhao@intel.com>
From: Linus Walleij <linus.walleij@linaro.org>
Date: Fri, 2 Feb 2024 18:43:00 +0100
Message-ID: <CACRpkdarfWFhvJ8vrDZXOk-nhDkgfwOLB+EytVm1S=-dEFKy3A@mail.gmail.com>
Subject: Re: [PATCH] mm: Remove broken pfn_to_virt() on arch csky/hexagon/openrisc
To: Yan Zhao <yan.y.zhao@intel.com>
Cc: arnd@arndb.de, guoren@kernel.org, bcain@quicinc.com, jonas@southpole.se, 
	stefan.kristiansson@saunalahti.fi, shorne@gmail.com, 
	linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, 
	linux-openrisc@vger.kernel.org
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On Fri, Feb 2, 2024 at 3:35=E2=80=AFPM Yan Zhao <yan.y.zhao@intel.com> wrot=
e:

> 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, whic=
h
> 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 i=
s
> 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.c=
om [1]
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Suggested-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>

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

Yours,
Linus Walleij