Re: [PATCH] sparc64: Swap registers for fault code and address in mna trap

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From	David Miller <davem@davemloft.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH] sparc64: Swap registers for fault code and address in mna trap
Date	Sat, 18 Jun 2016 08:20:01 +0200
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From: 神田　尚 <hikanda@zlab.co.jp>
Date: Fri, 17 Jun 2016 01:49:11 +0000

> This bug may occur in the following.
>
> user_rtt_fill_64bit          <= If mna trap occurred, call do_mna
> +-> do_mna                   <= Mistake storing registers for fault code and address
>     +-> winfix_mna
>         +-> user_rtt_fill_fixup  <= Put fault address into thread_info->flag's TI_FAULT_CODE 
>             +-> do_sparc64_fault() <= If fault address has FAULT_CODE_ITLB and FAULT_CODE_DTLB bits, call BUG()
>                 +-> BUG()

We should not be invoking do_sparc64_fault() in this case.

Instead, we call either sun4v_do_mna() or mem_address_unaligned().

Neither of which care about the values stored in the thread's fault
address and code.

If you can really trigger this code path, please post the kernel log
backtrace that happens when the BUG() triggers.  That way we can
figure out what the real problem is.

Your patch is also wrong for other reasons, it would break the
unaligned trap code paths that don't go via user_rtt_fill_64bit
fixups.

Thread

[PATCH] sparc64: Swap registers for fault code and address in mna  trap 神田　尚 <hikanda@zlab.co.jp> - 2016-06-17 03:50 +0200
  Re: [PATCH] sparc64: Swap registers for fault code and address in  mna trap David Miller <davem@davemloft.net> - 2016-06-18 08:20 +0200
    RE: [PATCH] sparc64: Swap registers for fault code and address in mna  trap 神田　尚 <hikanda@zlab.co.jp> - 2016-06-21 12:40 +0200
      Re: [PATCH] sparc64: Swap registers for fault code and address in  mna trap David Miller <davem@davemloft.net> - 2016-06-22 20:50 +0200

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