Messages in this thread | | | Subject | Re: [PATCH] powerpc/mm: tell if a bad page fault on data is read or write. | From | Christophe Leroy <> | Date | Fri, 30 Aug 2019 09:41:14 +0200 |
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Le 29/08/2019 à 14:14, Michael Ellerman a écrit : > 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().
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
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