On Mon, Mar 23, 2020 at 03:06:36PM -0400, Peter Xu wrote: > On Fri, Mar 20, 2020 at 01:55:46PM -0700, Sean Christopherson wrote: > > + /* > > + * Spin until the memory region is moved to a misaligned address. This > > + * may or may not trigger MMIO, as the window where the memslot is > > + * invalid is quite small. > > + */ > > + val = guest_spin_on_val(0); > > + GUEST_ASSERT(val == 1 || val == MMIO_VAL); > > + > > + /* Spin until the memory region is realigned. */ > > + GUEST_ASSERT(guest_spin_on_val(MMIO_VAL) == 1); > > IIUC ideally we should do GUEST_SYNC() after each GUEST_ASSERT() to > make sure the two threads are in sync. Otherwise e.g. there's no > guarantee that the main thread won't run too fast to quickly remove > the memslot and re-add it back before the guest_spin_on_val() starts > above, then the assert could trigger when it reads the value as zero. Hrm, I was thinking ucall wasn't available across pthreads, but it's just dumped into a global variable. I'll rework this to replace the udelay() hacks with proper synchronization.
