linux-kernel - Re: [PATCH] ARM: mm: support big-endian page tables

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Message-ID: <52F9FE1A.6000607@codethink.co.uk>
Date:	Tue, 11 Feb 2014 10:40:26 +0000
From:	Ben Dooks <ben.dooks@...ethink.co.uk>
To:	Jianguo Wu <wujianguo@...wei.com>
CC:	linux@....linux.org.uk, will.deacon@....com,
	gregkh@...uxfoundation.org,
	Catalin Marinas <catalin.marinas@....com>,
	Li Zefan <lizefan@...wei.com>, Wang Nan <wangnan0@...wei.com>,
	linux-arm-kernel@...ts.infradead.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] ARM: mm: support big-endian page tables

On 11/02/14 09:20, Jianguo Wu wrote:
> When enable LPAE and big-endian in a hisilicon board, while specify
> mem=384M mem=512M@...0M, will get bad page state:
>
> Freeing unused kernel memory: 180K (c0466000 - c0493000)
> BUG: Bad page state in process init  pfn:fa442
> page:c7749840 count:0 mapcount:-1 mapping:  (null) index:0x0
> page flags: 0x40000400(reserved)
> Modules linked in:
> CPU: 0 PID: 1 Comm: init Not tainted 3.10.27+ #66
> [<c000f5f0>] (unwind_backtrace+0x0/0x11c) from [<c000cbc4>] (show_stack+0x10/0x14)
> [<c000cbc4>] (show_stack+0x10/0x14) from [<c009e448>] (bad_page+0xd4/0x104)
> [<c009e448>] (bad_page+0xd4/0x104) from [<c009e520>] (free_pages_prepare+0xa8/0x14c)
> [<c009e520>] (free_pages_prepare+0xa8/0x14c) from [<c009f8ec>] (free_hot_cold_page+0x18/0xf0)
> [<c009f8ec>] (free_hot_cold_page+0x18/0xf0) from [<c00b5444>] (handle_pte_fault+0xcf4/0xdc8)
> [<c00b5444>] (handle_pte_fault+0xcf4/0xdc8) from [<c00b6458>] (handle_mm_fault+0xf4/0x120)
> [<c00b6458>] (handle_mm_fault+0xf4/0x120) from [<c0013754>] (do_page_fault+0xfc/0x354)
> [<c0013754>] (do_page_fault+0xfc/0x354) from [<c0008400>] (do_DataAbort+0x2c/0x90)
> [<c0008400>] (do_DataAbort+0x2c/0x90) from [<c0008fb4>] (__dabt_usr+0x34/0x40)
>
> The bad pfn:fa442 is not system memory(mem=384M mem=512M@...0M), after debugging,
> I find in page fault handler, will get wrong pfn from pte just after set pte,
> as follow:
> do_anonymous_page()
> {
> 	...
> 	set_pte_at(mm, address, page_table, entry);
> 	
> 	//debug code
> 	pfn = pte_pfn(entry);
> 	pr_info("pfn:0x%lx, pte:0x%llx\n", pfn, pte_val(entry));
>
> 	//read out the pte just set
> 	new_pte = pte_offset_map(pmd, address);
> 	new_pfn = pte_pfn(*new_pte);
> 	pr_info("new pfn:0x%lx, new pte:0x%llx\n", pfn, pte_val(entry));
> 	...
> }

Thanks, must have missed tickling this one.

>
> pfn:   0x1fa4f5,     pte:0xc00001fa4f575f
> new_pfn:0xfa4f5, new_pte:0xc00000fa4f5f5f	//new pfn/pte is wrong.
>
> The bug is happened in cpu_v7_set_pte_ext(ptep, pte):
> when pte is 64-bit, for little-endian, will store low 32-bit in r2,
> high 32-bit in r3; for big-endian, will store low 32-bit in r3,
> high 32-bit in r2, this will cause wrong pfn stored in pte,
> so we should exchange r2 and r3 for big-endian.
>
> Signed-off-by: Jianguo Wu <wujianguo@...wei.com>
> ---
>   arch/arm/mm/proc-v7-3level.S |   10 ++++++++++
>   1 files changed, 10 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/mm/proc-v7-3level.S b/arch/arm/mm/proc-v7-3level.S
> index 6ba4bd9..71b3892 100644
> --- a/arch/arm/mm/proc-v7-3level.S
> +++ b/arch/arm/mm/proc-v7-3level.S
> @@ -65,6 +65,15 @@ ENDPROC(cpu_v7_switch_mm)
>    */
>   ENTRY(cpu_v7_set_pte_ext)
>   #ifdef CONFIG_MMU
> +#ifdef CONFIG_CPU_ENDIAN_BE8
> +	tst	r3, #L_PTE_VALID
> +	beq	1f
> +	tst	r2, #1 << (57 - 32)		@ L_PTE_NONE
> +	bicne	r3, #L_PTE_VALID
> +	bne	1f
> +	tst	r2, #1 << (55 - 32)		@ L_PTE_DIRTY
> +	orreq	r3, #L_PTE_RDONLY
> +#else
>   	tst	r2, #L_PTE_VALID
>   	beq	1f
>   	tst	r3, #1 << (57 - 32)		@ L_PTE_NONE
> @@ -72,6 +81,7 @@ ENTRY(cpu_v7_set_pte_ext)
>   	bne	1f
>   	tst	r3, #1 << (55 - 32)		@ L_PTE_DIRTY
>   	orreq	r2, #L_PTE_RDONLY
> +#endif
>   1:	strd	r2, r3, [r0]
>   	ALT_SMP(W(nop))
>   	ALT_UP (mcr	p15, 0, r0, c7, c10, 1)		@ flush_pte
> -- 1.7.1

If possible can we avoid large #ifdef blocks here?

Two ideas are

ARM_LE(tst r2, #L_PTE_VALID)
ARM_BE(tst r3, #L_PTE_VALID)

or change r2, r3 pair to say rlow, rhi and

#ifdef  CONFIG_CPU_ENDIAN_BE8
#define rlow r3
#define rhi r2
#else
#define rlow r2
#define rhi r3
#endif



-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius
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