On 03/17/2015 03:36 PM, Ingo Molnar wrote: > > * 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?
Sounds good to me. -- 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/
