On Thu, Jan 23, 2025 at 09:31:31AM +0100, Peter Zijlstra wrote: > On Wed, Jan 22, 2025 at 02:36:25PM -0800, Josh Poimboeuf wrote: > > On Wed, Jan 22, 2025 at 02:57:00PM +0100, Peter Zijlstra wrote: > > > On Tue, Jan 21, 2025 at 06:31:21PM -0800, Josh Poimboeuf wrote: > > But if the NMI happens late in the exit-to-user path, with IRQs > > disabled, right before nr_entries gets cleared, the cache won't get > > used in the task work. > > > > However I think we can clear it on entry-from-user. > > Return to user runs with interrupts disabled, if an NMI hits that, it > will have to set TIF_NOTIFY_RESUME again and queue the IRQ work thing. > That self-IPI will hit the moment we do IRET (which is what re-enables > interrupts) and we're going back into the kernel. > > Anyway, I suppose that is a long way of saying that you should be able > to do this on return to user.
Indeed, I knew that but somehow overlooked the fact that the IRQ would clear the cookie so the cache wouldn't be usable anyway. -- Josh
