From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/mm: tell if a bad page fault on data is read or write.
Date: Thu, 29 Aug 2019 14:59:00 +0200 [thread overview]
Message-ID: <5f539c22-532a-3319-afe8-cdfac4ab3ee6@c-s.fr> (raw)
In-Reply-To: <87o908tbgx.fsf@mpe.ellerman.id.au>
Le 29/08/2019 à 14:14, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>> DSISR has a bit to tell if the fault is due to a read or a write.
>
> Except some CPUs don't have a DSISR?
>
> Which is why we have page_fault_is_write() that's used in
> __do_page_fault().
>
> Or is that old cruft?
>
> I see eg. in head_40x.S we pass r5=0 for error code, and we don't set
> regs->dsisr anywhere AFAICS. So it might just contain some junk.
But then we have a problem with show_regs() as well, havent't we ?
if (trap == 0x200 || trap == 0x300 || trap == 0x600)
#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
pr_cont("DEAR: "REG" ESR: "REG" ", regs->dar, regs->dsisr);
#else
pr_cont("DAR: "REG" DSISR: %08lx ", regs->dar, regs->dsisr);
#endif
I need to look closer.
Christophe
>
> cheers
>
>> 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
next prev parent reply other threads:[~2019-08-29 13:03 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-21 15:21 [PATCH] powerpc/mm: tell if a bad page fault on data is read or write Christophe Leroy
2019-08-26 5:35 ` Santosh Sivaraj
2019-08-29 12:14 ` Michael Ellerman
2019-08-29 12:59 ` Christophe Leroy [this message]
2019-08-30 7:41 ` Christophe Leroy
2019-11-25 10:46 ` Michael Ellerman
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