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

From: Christophe Leroy
Date: Thu Aug 29 2019 - 08:59:04 EST

Le 29/08/2019 Ã 14:14, Michael Ellerman a ÃcritÂ:
Christophe Leroy <christophe.leroy@xxxxxx> 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

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);
pr_cont("DAR: "REG" DSISR: %08lx ", regs->dar, regs->dsisr);

I need to look closer.



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);

case 0x400:
case 0x480: