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SubjectRe: [PATCHv2] arm: LPAE: kexec: clear TTBCR.T1SZ explicitly when PHYS_OFFSET > PAGE_OFFSET
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On 05/06/17 11:06, Hoeun Ryu wrote:
> Clearing TTBCR.T1SZ explicitly when kernel runs on a configuration of
> PHYS_OFFSET > PAGE_OFFSET.
> Reading TTBCR in early boot stage might returns the value of the
> previous kernel's configuration, especially in case of kexec. For
> example, if normal kernel (first kernel) had run on a configuration
> of PHYS_OFFSET <= PAGE_OFFSET and crash kernel (second kernel) is
> running on a configuration PHYS_OFFSET > PAGE_OFFSET, which can happen
> because it depends on the reserved area for crash kernel, reading
> TTBCR and using the value without clearing TTBCR.T1SZ might risky
> because the value doesn't have a reset value for TTBCR.T1SZ.

Hmm, but isn't that also strictly true of all the other fields we're
ORing TTB_FLAGS_* into? Given that this is initial setup, I wonder
whether we need to care about the previous TTBCR value at all - is there
any reason for not simply building up the value we want from scratch?

Robin.

> Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com>
> ---
> arch/arm/mm/proc-v7-3level.S | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm/mm/proc-v7-3level.S b/arch/arm/mm/proc-v7-3level.S
> index 5e5720e..81404b8 100644
> --- a/arch/arm/mm/proc-v7-3level.S
> +++ b/arch/arm/mm/proc-v7-3level.S
> @@ -140,6 +140,7 @@ ENDPROC(cpu_v7_set_pte_ext)
> * otherwise booting secondary CPUs would end up using TTBR1 for the
> * identity mapping set up in TTBR0.
> */
> + bichi \tmp, \tmp, #(7 << 16) @ clear TTBCR.T1SZ
> orrls \tmp, \tmp, #TTBR1_SIZE @ TTBCR.T1SZ
> mcr p15, 0, \tmp, c2, c0, 2 @ TTBCR
> mov \tmp, \ttbr1, lsr #20
>

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