On Thu, Jan 22, 2015 at 1:16 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Thu, 22 Jan 2015 12:58:00 -0800 > Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > >> On Thu, Jan 22, 2015 at 12:37 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: >> > On Thu, 22 Jan 2015 12:24:47 -0800 >> > Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> >> >> >> >> The other issue, above and beyond RCU, is that we can't let kprobes >> >> run on the int3 stack. If Xen upcalls can happen when interrupts are >> >> off, then we may need this protection to prevent that type of >> >> recursion. (This will be much less scary in 3.20, because userspace >> >> int3 instructions will no longer execute on the int3 stack.) >> > >> > Does this execute between the start of the int3 interrupt handler and >> > the call of do_int3()? >> >> I doubt it. >> >> The thing I worry about is that, if do_int3 nests inside itself by any >> means (e.g. int3 sends a signal, scheduling for whatever reason >> (really shouldn't happen, but I haven't looked that hard)), then we're >> completely hosed -- the inner int3 will overwrite the outer int3's >> stack frame. Since I have no idea what Xen upcalls do, I don't know >> whether they can fire inside do_int3. > > I thought there's logic in the do_int3 handler (in the assembly code) > that can handle nested int3s. Nope :( In 3.20, there's likely to be logic that can handle a single level of nesting as long as the outer one came from user space. --Andy -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
