On Wed, Aug 24, 2022, Oliver Upton wrote: > Hi Sean, > > On Wed, Aug 24, 2022 at 03:21:14AM +0000, Sean Christopherson wrote: > > +/* > > + * Sync a global pointer to the guest that has a per-VM value, in which case > > + * writes to the host copy of the "global" must be serialized (in case a test > > + * is being truly crazy and spawning multiple VMs concurrently). > > + */ > > Do we even care about writes to the host's copy of the global pointer? > I don't see how the host pointer is used beyond serializing writes into > a guest. > > IOW, it looks as though we could skip the whole global illusion > altogether and write straight into guest memory. *sigh* This exact thought crossed my mind when I first looked at this code, but somehow I couldn't come up with the obvious solution of using a temporary on-stack variable to hold the desired value. Something like this should work. #define write_guest_global(vm, g, val) ({ \ typeof(g) *_p = addr_gva2hva(vm, (vm_vaddr_t)&(g)); \ typeof(g) _val = val; \ \ memcpy(_p, &(_val), sizeof(g)); \ })