linux-kernel - Re: [PATCH] powerpc/mm: tell if a bad page fault on data is read or write.

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Date:   Mon, 26 Aug 2019 11:05:56 +0530
From:   Santosh Sivaraj <santosh@...six.org>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/mm: tell if a bad page fault on data is read or write.

Christophe Leroy <christophe.leroy@....fr> writes:

> DSISR has a bit to tell if the fault is due to a read or a write.
>
> Display it.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Reviewed-by: Santosh Sivaraj <santosh@...six.org>

> ---
>  arch/powerpc/mm/fault.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 8432c281de92..b5047f9b5dec 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -645,6 +645,7 @@ NOKPROBE_SYMBOL(do_page_fault);
>  void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
>  {
>  	const struct exception_table_entry *entry;
> +	int is_write = page_fault_is_write(regs->dsisr);
>  
>  	/* Are we prepared to handle this fault?  */
>  	if ((entry = search_exception_tables(regs->nip)) != NULL) {
> @@ -658,9 +659,10 @@ void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
>  	case 0x300:
>  	case 0x380:
>  	case 0xe00:
> -		pr_alert("BUG: %s at 0x%08lx\n",
> +		pr_alert("BUG: %s on %s at 0x%08lx\n",
>  			 regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" :
> -			 "Unable to handle kernel data access", regs->dar);
> +			 "Unable to handle kernel data access",
> +			 is_write ? "write" : "read", regs->dar);
>  		break;
>  	case 0x400:
>  	case 0x480:
> -- 
> 2.13.3