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

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

Display it.

Signed-off-by: Christophe Leroy <redacted>
---
 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

Christophe Leroy [off-list ref] 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 <redacted>

Reviewed-by: Santosh Sivaraj <redacted>

Christophe Leroy [off-list ref] 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

 		break;
 	case 0x400:
 	case 0x480:
-- 
2.13.3

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

Christophe Leroy [off-list ref] writes:

quoted

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

quoted

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);

quoted

  		break;
  	case 0x400:
  	case 0x480:
-- 
2.13.3

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

Christophe Leroy [off-list ref] writes:

quoted

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

quoted

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);

quoted

  		break;
  	case 0x400:
  	case 0x480:
-- 
2.13.3

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 <redacted>

Applied to powerpc next, thanks.

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

cheers