Re: [RFC PATCH -next V2 2/7] arm64: fix page_address return value in copy_highpage

From: Mark Rutland <mark.rutland@arm.com>
To: Tong Tiangen <tongtiangen@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Vincenzo Frascino <vincenzo.frascino@arm.com>
Subject: Re: [RFC PATCH -next V2 2/7] arm64: fix page_address return value in copy_highpage
Date: Wed, 6 Apr 2022 11:22:07 +0100	[thread overview]
Message-ID: <Yk1pz7IYwEyGDVNV@FVFF77S0Q05N> (raw)
In-Reply-To: <20220406091311.3354723-3-tongtiangen@huawei.com>

On Wed, Apr 06, 2022 at 09:13:06AM +0000, Tong Tiangen wrote:
> Function page_address return void, fix it.
> 
> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>

This looks like a sensible cleanup, but the commit title and message aren't
that clear.

Can you please make this:

| arm64: fix types in copy_highpage()
|
| In copy_highpage() the `kto` and `kfrom` local variables are pointers to
| struct page, but these are used to hold arbitrary pointers to kernel memory.
| Each call to page_address() returns a void pointer to memory associated with
| the relevant page, and copy_page() expects void pointers to this memory.
|
| This inconsistency was introduced in commit:
|
|   2563776b41c31908 ("arm64: mte: Tags-aware copy_{user_,}highpage() implementations")
|
| ... and while this doesn't appear to be harmful in practice it is clearly wrong.
|
| Correct this by making `kto` and `kfrom` void pointers.
|
| Fixes: 2563776b41c31908 ("arm64: mte: Tags-aware copy_{user_,}highpage() implementations")

With that:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Thanks,
Mark.

> ---
>  arch/arm64/mm/copypage.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c
> index b5447e53cd73..0dea80bf6de4 100644
> --- a/arch/arm64/mm/copypage.c
> +++ b/arch/arm64/mm/copypage.c
> @@ -16,8 +16,8 @@
>  
>  void copy_highpage(struct page *to, struct page *from)
>  {
> -	struct page *kto = page_address(to);
> -	struct page *kfrom = page_address(from);
> +	void *kto = page_address(to);
> +	void *kfrom = page_address(from);
>  
>  	copy_page(kto, kfrom);
>  
> -- 
> 2.18.0.huawei.25
> 
> 
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