Re: [PATCH 3/5] arm64: mte: Define the number of bytes for storing the tags in a page

From: Luis Machado <luis.machado@linaro.org>
To: Catalin Marinas <catalin.marinas@arm.com>,
	linux-arm-kernel@lists.infradead.org
Cc: Will Deacon <will@kernel.org>, John Baldwin <jhb@FreeBSD.org>,
	Arnd Bergmann <arnd@arndb.de>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Kees Cook <keescook@chromium.org>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 3/5] arm64: mte: Define the number of bytes for storing the tags in a page
Date: Mon, 3 Jan 2022 14:27:58 -0300	[thread overview]
Message-ID: <decd67e4-e659-18bd-c848-f840cda98ba4@linaro.org> (raw)
In-Reply-To: <20211208121941.494956-4-catalin.marinas@arm.com>

On 12/8/21 9:19 AM, Catalin Marinas wrote:
> Rather than explicitly calculating the number of bytes for a compact tag
> storage format corresponding to a page, just add a MTE_PAGE_TAG_STORAGE
> macro. With the current MTE implementation of 4 bits per tag, we store
> 2 tags in a byte.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> ---
>   arch/arm64/include/asm/mte-def.h | 1 +
>   arch/arm64/lib/mte.S             | 4 ++--
>   arch/arm64/mm/mteswap.c          | 2 +-
>   3 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/mte-def.h b/arch/arm64/include/asm/mte-def.h
> index 626d359b396e..14ee86b019c2 100644
> --- a/arch/arm64/include/asm/mte-def.h
> +++ b/arch/arm64/include/asm/mte-def.h
> @@ -11,6 +11,7 @@
>   #define MTE_TAG_SHIFT		56
>   #define MTE_TAG_SIZE		4
>   #define MTE_TAG_MASK		GENMASK((MTE_TAG_SHIFT + (MTE_TAG_SIZE - 1)), MTE_TAG_SHIFT)
> +#define MTE_PAGE_TAG_STORAGE	(MTE_GRANULES_PER_PAGE * MTE_TAG_SIZE / 8)
>   
>   #define __MTE_PREAMBLE		ARM64_ASM_PREAMBLE ".arch_extension memtag\n"
>   
> diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
> index e83643b3995f..62a1025aa118 100644
> --- a/arch/arm64/lib/mte.S
> +++ b/arch/arm64/lib/mte.S
> @@ -128,7 +128,7 @@ SYM_FUNC_END(mte_copy_tags_to_user)
>   /*
>    * Save the tags in a page
>    *   x0 - page address
> - *   x1 - tag storage
> + *   x1 - tag storage, MTE_PAGE_TAG_STORAGE bytes
>    */
>   SYM_FUNC_START(mte_save_page_tags)
>   	multitag_transfer_size x7, x5
> @@ -152,7 +152,7 @@ SYM_FUNC_END(mte_save_page_tags)
>   /*
>    * Restore the tags in a page
>    *   x0 - page address
> - *   x1 - tag storage
> + *   x1 - tag storage, MTE_PAGE_TAG_STORAGE bytes
>    */
>   SYM_FUNC_START(mte_restore_page_tags)
>   	multitag_transfer_size x7, x5
> diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c
> index 7c4ef56265ee..a9e50e930484 100644
> --- a/arch/arm64/mm/mteswap.c
> +++ b/arch/arm64/mm/mteswap.c
> @@ -12,7 +12,7 @@ static DEFINE_XARRAY(mte_pages);
>   void *mte_allocate_tag_storage(void)
>   {
>   	/* tags granule is 16 bytes, 2 tags stored per byte */
> -	return kmalloc(PAGE_SIZE / 16 / 2, GFP_KERNEL);
> +	return kmalloc(MTE_PAGE_TAG_STORAGE, GFP_KERNEL);
>   }
>   
>   void mte_free_tag_storage(char *storage)
> 

Acked-by: Luis Machado <luis.machado@linaro.org>

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