linux-kernel - Re: [PATCH v2 25/37] arm64: kasan: Enable in-kernel MTE

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Date:   Thu, 17 Sep 2020 17:35:37 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        kasan-dev@...glegroups.com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 25/37] arm64: kasan: Enable in-kernel MTE

On Tue, Sep 15, 2020 at 11:16:07PM +0200, Andrey Konovalov wrote:
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index 23c326a06b2d..5ba7ac5e9c77 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -427,6 +427,10 @@ SYM_FUNC_START(__cpu_setup)
>  	 */
>  	mov_q	x5, MAIR_EL1_SET
>  #ifdef CONFIG_ARM64_MTE
> +	mte_present	.req	x20
> +
> +	mov	mte_present, #0
> +
>  	/*
>  	 * Update MAIR_EL1, GCR_EL1 and TFSR*_EL1 if MTE is supported
>  	 * (ID_AA64PFR1_EL1[11:8] > 1).
> @@ -447,6 +451,8 @@ SYM_FUNC_START(__cpu_setup)
>  	/* clear any pending tag check faults in TFSR*_EL1 */
>  	msr_s	SYS_TFSR_EL1, xzr
>  	msr_s	SYS_TFSRE0_EL1, xzr
> +
> +	mov	mte_present, #1
>  1:
>  #endif
>  	msr	mair_el1, x5
> @@ -485,6 +491,13 @@ SYM_FUNC_START(__cpu_setup)
>  	orr	x10, x10, #TCR_HA		// hardware Access flag update
>  1:
>  #endif	/* CONFIG_ARM64_HW_AFDBM */
> +#ifdef CONFIG_ARM64_MTE
> +	/* Update TCR_EL1 if MTE is supported (ID_AA64PFR1_EL1[11:8] > 1) */
> +	cbz	mte_present, 1f
> +	orr	x10, x10, #SYS_TCR_EL1_TCMA1
> +1:
> +	.unreq	mte_present
> +#endif
>  	msr	tcr_el1, x10
>  	/*
>  	 * Prepare SCTLR

I'd keep this simpler, no branches or #ifdefs (you can still add the
.req if you want):

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 23c326a06b2d..a35344754081 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -426,6 +426,7 @@ SYM_FUNC_START(__cpu_setup)
 	 * Memory region attributes
 	 */
 	mov_q	x5, MAIR_EL1_SET
+	mov	x8, #0
 #ifdef CONFIG_ARM64_MTE
 	/*
 	 * Update MAIR_EL1, GCR_EL1 and TFSR*_EL1 if MTE is supported
@@ -447,6 +448,9 @@ SYM_FUNC_START(__cpu_setup)
 	/* clear any pending tag check faults in TFSR*_EL1 */
 	msr_s	SYS_TFSR_EL1, xzr
 	msr_s	SYS_TFSRE0_EL1, xzr
+
+	/* set the TCR_EL1 bits */
+	orr	x8, x8, #SYS_TCR_EL1_TCMA1
 1:
 #endif
 	msr	mair_el1, x5
@@ -457,6 +461,7 @@ SYM_FUNC_START(__cpu_setup)
 	mov_q	x10, TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
 			TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
 			TCR_TBI0 | TCR_A1 | TCR_KASAN_FLAGS
+	orr	x10, x10, x8
 	tcr_clear_errata_bits x10, x9, x5
 
 #ifdef CONFIG_ARM64_VA_BITS_52

-- 
Catalin