On Fri, Jun 11, 2021 at 04:05:15PM +0200, Borislav Petkov wrote: > On Thu, Jun 10, 2021 at 11:11:37AM +0200, Joerg Roedel wrote: > Why not simply "sandwich" them: > > local_irq_save() > sev_es_get_ghcb() > > ...blablabla > > sev_es_put_ghcb() > local_irq_restore(); > > in every call site? I am not a fan of this, because its easily forgotten to add local_irq_save()/local_irq_restore() calls around those. Yes, we can add irqs_disabled() assertions to the functions, but we can as well just disable/enable IRQs in them. Only the previous value of EFLAGS.IF needs to be carried from one function to the other. > Hmm, so why aren't you accessing/setting data->ghcb_active and > data->backup_ghcb_active safely using cmpxchg() if this path can be > interrupted by an NMI? Using cmpxchg is not necessary here. It is all per-cpu data, so local to the current cpu. If an NMI happens anywhere in sev_es_get_ghcb() it can still use the GHCB, because the interrupted #VC handler will not start writing to it before sev_es_get_ghcb() returned. Problems only come up when one path starts writing to the GHCB, but that happens long after it is marked active. Regards, Joerg
