[PATCH] arm64: fix invalidation of wrong __early_cpu_boot_status cacheline

[Mark Rutland]

On Fri, Apr 15, 2016 at 12:11:21PM +0200, Ard Biesheuvel wrote:
> In head.S, the str_l macro, which takes a source register, a symbol name
> and a temp register, is used to store a status value to the variable
> __early_cpu_boot_status. Subsequently, the value of the temp register is
> reused to invalidate any cachelines covering this variable.
> 
> However, since str_l resolves to
> 
>       adrp    \tmp, \sym
>       str     \src, [\tmp, :lo12:\sym]
> 
> the temp register never actually holds the address of the variable but
> only of the 4 KB window that covers it, and reusing it leads to the
> wrong cacheline being invalidated. So instead, take the address
> explicitly before doing the store, and reuse that value to perform
> the cache invalidation.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
> 
> This deserves a cc stable, since the macro is always invoked for each CPU
> at boot.

Sounds good, also:

Fixes: bb9052744f4b7ae1 ("arm64: Handle early CPU boot failures")

> Alternatively, we could add a writeback to the str_l macro, but I think
> in general, making any assumptions about the value of a temp register is
> dodgy, so I prefer this approach instead.

Likewise, I prefer this.

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

Mark.

>  arch/arm64/kernel/head.S | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 8b8a3d1e23fb..fafe21e49aab 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -693,7 +693,8 @@ ENDPROC(__secondary_switched)
>  
>  	.macro	update_early_cpu_boot_status status, tmp1, tmp2
>  	mov	\tmp2, #\status
> -	str_l	\tmp2, __early_cpu_boot_status, \tmp1
> +	adr_l	\tmp1, __early_cpu_boot_status
> +	str	\tmp2, [\tmp1]
>  	dmb	sy
>  	dc	ivac, \tmp1			// Invalidate potentially stale cache line
>  	.endm
> -- 
> 2.5.0
> 
> 
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