linux-kernel - Re: [PATCH] arm:lpae: build TTB control register value from scratch in v7_ttb

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Date:   Sat, 10 Jun 2017 13:43:24 +0900
From:   Hoeun Ryu <hoeun.ryu@...il.com>
To:     Robin Murphy <robin.murphy@....com>,
        Russell King <linux@...linux.org.uk>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm:lpae: build TTB control register value from scratch in v7_ttb_setup

Hello, Russell and Robin.

Would you please review this patch ?

Than you

> On Jun 7, 2017, at 11:39 AM, Hoeun Ryu <hoeun.ryu@...il.com> wrote:
> 
> Reading TTBCR in early boot stage might return 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 to OR
> other bit fields might be risky because it doesn't have a reset value for
> TTBCR.
> 
> Suggested-by: Robin Murphy <robin.murphy@....com>
> Signed-off-by: Hoeun Ryu <hoeun.ryu@...il.com>
> ---
> 
> * v1: amended based on
>          - "[PATCHv2] arm: LPAE: kexec: clear TTBCR.T1SZ explicitly when
>             PHYS_OFFSET > PAGE_OFFSET"
>          - https://lkml.org/lkml/2017/6/5/239
> 
> arch/arm/mm/proc-v7-3level.S | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/arm/mm/proc-v7-3level.S b/arch/arm/mm/proc-v7-3level.S
> index 5e5720e..7d16bbc 100644
> --- a/arch/arm/mm/proc-v7-3level.S
> +++ b/arch/arm/mm/proc-v7-3level.S
> @@ -129,8 +129,7 @@ ENDPROC(cpu_v7_set_pte_ext)
>    .macro    v7_ttb_setup, zero, ttbr0l, ttbr0h, ttbr1, tmp
>    ldr    \tmp, =swapper_pg_dir        @ swapper_pg_dir virtual address
>    cmp    \ttbr1, \tmp, lsr #12        @ PHYS_OFFSET > PAGE_OFFSET?
> -    mrc    p15, 0, \tmp, c2, c0, 2        @ TTB control egister
> -    orr    \tmp, \tmp, #TTB_EAE
> +    mov    \tmp, #TTB_EAE            @ for TTB control egister
>    ALT_SMP(orr    \tmp, \tmp, #TTB_FLAGS_SMP)
>    ALT_UP(orr    \tmp, \tmp, #TTB_FLAGS_UP)
>    ALT_SMP(orr    \tmp, \tmp, #TTB_FLAGS_SMP << 16)
> -- 
> 2.7.4
>