linux-kernel - Re: [RFC V3 07/13] arm64/mm: Add FEAT

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Date:   Tue, 12 Oct 2021 11:41:47 +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
Cc:     mark.rutland@....com, will@...nel.org, catalin.marinas@....com,
        maz@...nel.org, james.morse@....com, steven.price@....com
Subject: Re: [RFC V3 07/13] arm64/mm: Add FEAT_LPA2 specific encoding

On 30/09/2021 11:35, Anshuman Khandual wrote:
> FEAT_LPA2 requires different PTE representation formats for both 4K and 16K
> page size config. This adds FEAT_LPA2 specific new PTE encodings as per ARM
> ARM (0487G.A) which updates [pte|phys]_to_[phys|pte](). The updated helpers
> would be used when FEAT_LPA2 gets enabled via CONFIG_ARM64_PA_BITS_52 on 4K
> and 16K page size. Although TTBR encoding and phys_to_ttbr() helper remains
> the same as FEAT_LPA for FEAT_LPA2 as well. It updates 'phys_to_pte' helper
> to accept a temporary variable and changes impacted call sites.
> 
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>   arch/arm64/include/asm/assembler.h     | 14 +++++++++++---
>   arch/arm64/include/asm/pgtable-hwdef.h |  4 ++++
>   arch/arm64/include/asm/pgtable.h       |  4 ++++
>   3 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index 3fbe04a..c1543067 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -628,6 +628,10 @@ alternative_endif
>   	 */
>   	orr	\pte, \phys, \phys, lsr #36
>   	and	\pte, \pte, #PTE_ADDR_MASK
> +#elif defined(CONFIG_ARM64_PA_BITS_52_LPA2)
> +	orr	\pte, \phys, \phys, lsr #42
> +	and	\pte, \pte, #PTE_ADDR_MASK | GENMASK(PAGE_SHIFT - 1, 10)
> +	and	\pte, \pte, #~GENMASK(PAGE_SHIFT - 1, 10)
>   #else  /* !CONFIG_ARM64_PA_BITS_52_LPA */
>   	mov	\pte, \phys
>   #endif /* CONFIG_ARM64_PA_BITS_52_LPA */
> @@ -635,9 +639,13 @@ alternative_endif
>   
>   	.macro	pte_to_phys, phys, pte
>   #ifdef CONFIG_ARM64_PA_BITS_52_LPA
> -	ubfiz	\phys, \pte, #(48 - 16 - 12), #16
> -	bfxil	\phys, \pte, #16, #32
> -	lsl	\phys, \phys, #16
> +	ubfiz	\phys, \pte, #(48 - PAGE_SHIFT - 12), #16
> +	bfxil	\phys, \pte, #PAGE_SHIFT, #(48 - PAGE_SHIFT)

nit: This looks like an unrelated change and is better suited for the 
previous patch.


Suzuki