On Mon, 20 Aug 2018 19:41:56 +1000
Nicholas Piggin <npig...@gmail.com> wrote:
> +long do_slb_fault(struct pt_regs *regs, unsigned long ea)
> +{
> + unsigned long id = REGION_ID(ea);
> +
> + /* IRQs are not reconciled here, so can't check irqs_disabled */
> + VM_WARN_ON(mfmsr() & MSR_EE);
> +
> + /*
> + * SLB kernel faults must be very careful not to touch anything
> + * that is not bolted. E.g., PACA and global variables are okay,
> + * mm->context stuff is not.
> + *
> + * SLB user faults can access all of kernel memory, but must be
> + * careful not to touch things like IRQ state because it is not
> + * "reconciled" here. The difficulty is that we must use
> + * fast_exception_return to return from kernel SLB faults without
> + * looking at possible non-bolted memory. We could test user vs
> + * kernel faults in the interrupt handler asm and do a full fault,
> + * reconcile, ret_from_except for user faults which would make them
> + * first class kernel code. But for performance it's probably nicer
> + * if they go via fast_exception_return too.
> + */
> + if (id >= KERNEL_REGION_ID) {
> + return slb_allocate_kernel(ea, id);
> + } else {
> + struct mm_struct *mm = current->mm;
> +
> + if (unlikely(!mm))
> + return -EFAULT;
>
> - handle_multi_context_slb_miss(context, ea);
> - exception_exit(prev_state);
> - return;
> + return slb_allocate_user(mm, ea);
> + }
> +}
>
> -slb_bad_addr:
> +void do_bad_slb_fault(struct pt_regs *regs, unsigned long ea, long err)
> +{
> if (user_mode(regs))
> _exception(SIGSEGV, regs, SEGV_BNDERR, ea);
> else
> bad_page_fault(regs, ea, SIGSEGV);
> - exception_exit(prev_state);
> }
I knew I forgot something -- forgot to test MSR[RI] here. That can be
done just by returning a different error from do_slb_fault if RI is
clear, and do_bad_slb_fault will call unrecoverable_exception() if it
sees that code.
Thanks,
Nick
