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Re: [PATCH] cleanup vmalloc_fault for 64bit kernel

To: David Daney <ddaney@caviumnetworks.com>
Subject: Re: [PATCH] cleanup vmalloc_fault for 64bit kernel
From: Wu Fei <at.wufei@gmail.com>
Date: Thu, 10 Sep 2009 19:42:38 +0800
Cc: Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org
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On Wed, Sep 09, 2009 at 08:35:26AM -0700, David Daney wrote:
> Wu Fei wrote:
>> 64bit kernel won't arrive vmalloc_fault, it's not necessary or possible
>> to copy the page table from init_mm.pgd. swapper_pg_dir, module_pg_dir
>> and the process's pgd represent the different virtual address area, and
>> the tlb exception handler accesses the suitable one directly.
>>
>> Signed-off-by: Wu Fei <at.wufei@gmail.com>
>> ---
>>  arch/mips/mm/fault.c |    6 +++---
>>  1 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c
>> index f956ecb..e769789 100644
>> --- a/arch/mips/mm/fault.c
>> +++ b/arch/mips/mm/fault.c
>> @@ -58,11 +58,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs, 
>> unsigned long write,
>>       * only copy the information from the master page table,
>>       * nothing more.
>>       */
>> +#ifdef CONFIG_32BIT
>>      if (unlikely(address >= VMALLOC_START && address <= VMALLOC_END))
>>              goto vmalloc_fault;
>> -#ifdef MODULE_START
>> -    if (unlikely(address >= MODULE_START && address < MODULE_END))
>> -            goto vmalloc_fault;
>>  #endif
>>  
>
> That is not correct.  You can still arrive at do_page_fault() from  
> faults in the vmalloc range.  We need to go directly to the panic code  

That's not a real problem, if do_page_fault() from faults in the vmalloc
range, find_vma() returns NULL and eventually it will arrive no_context.
But anyway, I think your patch is better and readable.

Thanks,
Wufei.

> as I did in my patch: Message-Id:  
> <1251931654-21268-1-git-send-email-ddaney@caviumnetworks.com>
>
> AKA: [PATCH] MIPS: Don't corrupt page tables on vmalloc fault.
>
>
>
>>      /*
>> @@ -203,6 +201,7 @@ do_sigbus:
>>      force_sig_info(SIGBUS, &info, tsk);
>>      return;
>> +#ifdef CONFIG_32BIT
>>  vmalloc_fault:
>>      {
>>              /*
>> @@ -241,4 +240,5 @@ vmalloc_fault:
>>                      goto no_context;
>>              return;
>>      }
>> +#endif
>>  }
>

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