On Thu, Jul 23, 2015 at 11:15:15AM +0100, James Hogan wrote:
> On 23/07/15 10:10, Ralf Baechle wrote:
> > Without this we end taking execeptions in an endless loop hanging the
> > thread.
>
> A little more explanation would be nice. Under what situations does this
> occur? Does this mean any VM_EXEC and !VM_READ page can't actually be
> faulted in without it being treated as an RI violation, or does it only
> affect when read from kernel emulation code?
> > - if (!(vma->vm_flags & VM_READ)) {
> > + if (!(vma->vm_flags & VM_READ) &&
> > + exception_epc(regs) != address) {
> > #if 0
> > pr_notice("Cpu%d[%s:%d:%0*lx:%ld:%0*lx] RI violation\n",
> > raw_smp_processor_id(),
> >
>
The general idea is the change the code to treat loads of an instruction
just like an instruction fetch. Which is achieved by adding the second
condition "exception_epc(regs) != address" to the if above.
exception_epc(regs) == address means
It would all be easier if Linux was enabling the separate exception codes
for read and execution failure but short of that, a test like above must
provide if a fault was an attempted instruction fetch or happend fetching
data.
Ralf
