[PATCH v2 2/2] arm64: mte: DC {GVA,GZVA} shouldn't be used when DCZID_EL0.DZP == 1

[Catalin Marinas]

On Sun, Nov 07, 2021 at 11:11:49PM -0800, Reiji Watanabe wrote:
> diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
> index e83643b3995f..e62c048af337 100644
> --- a/arch/arm64/lib/mte.S
> +++ b/arch/arm64/lib/mte.S
> @@ -43,17 +43,23 @@ SYM_FUNC_END(mte_clear_page_tags)
>   *	x0 - address to the beginning of the page
>   */
>  SYM_FUNC_START(mte_zero_clear_page_tags)
> +	and	x0, x0, #(1 << MTE_TAG_SHIFT) - 1	// clear the tag
>  	mrs	x1, dczid_el0
> +	tbnz	x1, #4, 2f	// Branch if DC GZVA is prohibited
>  	and	w1, w1, #0xf
>  	mov	x2, #4
>  	lsl	x1, x2, x1
> -	and	x0, x0, #(1 << MTE_TAG_SHIFT) - 1	// clear the tag
>  
>  1:	dc	gzva, x0
>  	add	x0, x0, x1
>  	tst	x0, #(PAGE_SIZE - 1)
>  	b.ne	1b
>  	ret
> +
> +2:	stzg	x0, [x0], #16

Nitpick: MTE_GRANULE_SIZE instead of 16.

> +	tst	x0, #(PAGE_SIZE - 1)
> +	b.ne	2b
> +	ret
>  SYM_FUNC_END(mte_zero_clear_page_tags)

We can use stz2g here since we know it's always a PAGE_SIZE and an even
number of tag granules.

-- 
Catalin