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

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