On Thu, May 14, 2020 at 10:08:37AM +0200, Vitaly Kuznetsov wrote: > Vivek Goyal <vgoyal@xxxxxxxxxx> writes: > > > On Wed, May 13, 2020 at 04:23:55PM +0200, Vitaly Kuznetsov wrote: > > > > [..] > >> >> Also, > >> >> kdump kernel may not even support APF so it will get very confused when > >> >> APF events get delivered. > >> > > >> > New kernel can just ignore these events if it does not support async > >> > pf? > >> > > >> > This is somewhat similar to devices still doing interrupts in new > >> > kernel. And solution for that seemed to be doing a "reset" of devices > >> > in new kernel. We probably need similar logic where in new kernel > >> > we simply disable "async pf" so that we don't get new notifications. > >> > >> Right and that's what we're doing - just disabling new notifications. > > > > Nice. > > > > So why there is a need to deliver "page ready" notifications > > to guest after guest has disabled async pf. Atleast kdump does not > > seem to need it. It will boot into second kernel anyway, irrespective > > of the fact whether it receives page ready or not. > > We don't deliver anything to the guest after it disables APF (neither > 'page ready' for what was previously missing, nor 'page not ready' for > new faults), kvm_arch_can_inject_async_page_present() is just another > misnomer, it should be named something like > 'kvm_arch_can_unqueue_async_page_present()' meaning that 'page ready' > notification can be 'unqueued' from internal KVM queue. We will either > deliver it (when guest has APF enabled) or just drop it (when guest has > APF disabled). The only case when it has to stay in the queue is when > guest has APF enabled and the slot is still busy (so it didn't get to > process a previously delivered notification). We will try to deliver it > again after guest writes to MSR_KVM_ASYNC_PF_ACK. This makes sense. Renaming this function to make it more clear will help understanding code better. Vivek
