powerpc/mm: tell if a bad page fault on data is read or write.
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Message ID 4f88d7e6fda53b5f80a71040ab400242f6c8cb93.1566400889.git.christophe.leroy@c-s.fr
State New
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  • powerpc/mm: tell if a bad page fault on data is read or write.
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Commit Message

Christophe Leroy Aug. 21, 2019, 3:21 p.m. UTC
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@c-s.fr>
---
 arch/powerpc/mm/fault.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Santosh Sivaraj Aug. 26, 2019, 5:35 a.m. UTC | #1
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.
>
> Display it.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Reviewed-by: Santosh Sivaraj <santosh@fossix.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
Michael Ellerman Aug. 29, 2019, 12:14 p.m. UTC | #2
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.

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
Christophe Leroy Aug. 29, 2019, 12:59 p.m. UTC | #3
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
Christophe Leroy Aug. 30, 2019, 7:41 a.m. UTC | #4
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().


And that's why I'm also using page_fault_is_write() in my patch.

> 
> 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.


We pass r5=0 in ISI but r5=SPRN_ESR in DSI.
And r5 is also saved into _ESR(r11)

And in asm-offset.c, we have:

	STACK_PT_REGS_OFFSET(_ESR, dsisr);

So regs->dsisr has the expected content.

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

Patch
diff mbox series

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: