Le 29/08/2019 à 14:14, Michael Ellerman a écrit :
Christophe Leroy <christophe.le...@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

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