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SubjectRe: [PATCH 2/8] arm64: kernel: use literal for relocated address of __secondary_switched
On Mon, Apr 18, 2016 at 05:09:42PM +0200, Ard Biesheuvel wrote:
> We can simply use a relocated 64-bit literal to store the address of
> __secondary_switched(), and the relocation code will ensure that it
> holds the correct value at secondary entry time, as long as we make sure
> that the literal is not dereferenced until after we have enabled the MMU.
>
> So jump via a small __secondary_switch() function covered by the ID map
> that performs the literal load and branch-to-register.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Neat!

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
> arch/arm64/kernel/head.S | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index ac27d8d937b2..f13276d4ca91 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -468,9 +468,7 @@ __mmap_switched:
> str x15, [x11, x23]
> b 0b
>
> -2: adr_l x8, kimage_vaddr // make relocated kimage_vaddr
> - dc cvac, x8 // value visible to secondaries
> - dsb sy // with MMU off
> +2:
> #endif
>
> adr_l sp, initial_sp, x4
> @@ -699,12 +697,9 @@ secondary_startup:
> adrp x26, swapper_pg_dir
> bl __cpu_setup // initialise processor
>
> - ldr x8, kimage_vaddr
> - ldr w9, 0f
> - sub x27, x8, w9, sxtw // address to jump to after enabling the MMU
> + adr_l x27, __secondary_switch // address to jump to after enabling the MMU
> b __enable_mmu
> ENDPROC(secondary_startup)
> -0: .long (_text - TEXT_OFFSET) - __secondary_switched
>
> __secondary_switched:
> adr_l x5, vectors
> @@ -806,3 +801,8 @@ __no_granule_support:
> wfi
> b 1b
> ENDPROC(__no_granule_support)
> +
> +__secondary_switch:
> + ldr x8, =__secondary_switched
> + br x8
> +ENDPROC(__secondary_switch)
> --
> 2.5.0
>

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