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SubjectRe: [RFC 07/10] arm64/mm: Detect and enable FEAT_LPA2
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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@arm.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

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