* Denys Vlasenko <dvlas...@redhat.com> wrote:
> Without this change, it is still not possible to get rid of
> PER_CPU_VAR(old_rsp) usage in switch_to: if preemption happens
> while we did not fetch PER_CPU_VAR(old_rsp) and stored it in pt_regs->sp,
> PER_CPU_VAR(old_rsp) gets corrupted by other task's user sp.
Well, wouldn't this be a much clearer explanation:
"We want to use PER_CPU_VAR(old_rsp) as a simple temporary register,
to shuffle user-space RSP into (and from) when we set up the system
call stack frame. At that point we cannot shuffle values into general
purpose registers, because we have not saved them yet.
To be able to do this shuffling into a memory location, we must be
atomic and must not be preempted while we do the shuffling, otherwise
the 'temporary' register gets overwritten by some other task's
temporary register contents ..."
Agreed?
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
