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SubjectRe: [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@7680M, 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@7680M), 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@huawei.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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