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

[Michael Ellerman]

On Wed, 2019-08-21 at 15:21:55 UTC, Christophe Leroy wrote:
> DSISR has a bit to tell if the fault is due to a read or a write.
> 
> Display it.
> 
> Signed-off-by: Christophe Leroy 

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/46ddcb3950a28c0df4815e8dbb8d4b91d5d9f22d

cheers

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

[Christophe Leroy]

Le 29/08/2019 à 14:14, Michael Ellerman a écrit :

Christophe Leroy  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

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

[Christophe Leroy]

Le 29/08/2019 à 14:14, Michael Ellerman a écrit :

Christophe Leroy  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

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

[Michael Ellerman]

Christophe Leroy  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

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

[Santosh Sivaraj]

Christophe Leroy  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 

Reviewed-by: Santosh Sivaraj 

> ---
>  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

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

[Christophe Leroy]

DSISR has a bit to tell if the fault is due to a read or a write.

Display it.

Signed-off-by: Christophe Leroy 
---
 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