linux-kernel - Re: [RFC 07/10] arm64/mm: Detect and enable FEAT

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Date:   Wed, 14 Jul 2021 09:21:00 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, mark.rutland@....com, will@...nel.org,
        catalin.marinas@....com, maz@...nel.org, james.morse@....com,
        steven.price@....com
Subject: Re: [RFC 07/10] arm64/mm: Detect and enable FEAT_LPA2

On 14/07/2021 03:21, Anshuman Khandual wrote:
> Detect FEAT_LPA2 implementation early enough during boot when requested via
> CONFIG_ARM64_PA_BITS_52_LPA2 and remember in a variable arm64_lpa2_enabled.
> This variable could then be used to turn on TCR_EL1.TCR_DS effecting the 52
> bits PA range or fall back to default 48 bits PA range if FEAT_LPA2 feature
> was requested but found not to be implemented.
> 
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>   arch/arm64/include/asm/memory.h |  1 +
>   arch/arm64/kernel/head.S        | 15 +++++++++++++++
>   arch/arm64/mm/mmu.c             |  3 +++
>   arch/arm64/mm/proc.S            |  9 +++++++++
>   4 files changed, 28 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 824a365..d0ca002 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -178,6 +178,7 @@
>   #include <asm/bug.h>
>   
>   extern u64			vabits_actual;
> +extern u64			arm64_lpa2_enabled;
>   
>   extern s64			memstart_addr;
>   /* PHYS_OFFSET - the physical address of the start of memory. */
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 6444147..9cf79ea 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -94,6 +94,21 @@ SYM_CODE_START(primary_entry)
>   	adrp	x23, __PHYS_OFFSET
>   	and	x23, x23, MIN_KIMG_ALIGN - 1	// KASLR offset, defaults to 0
>   	bl	set_cpu_boot_mode_flag
> +
> +#ifdef CONFIG_ARM64_PA_BITS_52_LPA2
> +	mrs     x10, ID_AA64MMFR0_EL1
> +	ubfx    x10, x10, #ID_AA64MMFR0_TGRAN_SHIFT, 4
> +	cmp     x10, #ID_AA64MMFR0_TGRAN_LPA2
> +	b.ne	1f

For the sake of forward compatibility, this should be "b.lt"

Suzuki