2018-02-14 0:02 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: > On 05/02/2018 07:57, Wanpeng Li wrote: >> From: Wanpeng Li <wanpengli@xxxxxxxxxxx> >> >> If host CPUs are dedicated to a VM, we can avoid VM exits on HLT. >> This patch adds the per-VM non-HLT-exiting capability. >> >> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> >> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> >> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> >> --- >> v1 -> v2: >> * vmx_clear_hlt() around INIT handling >> * vmx_clear_hlt() upon SMI and implement auto halt restart > > Hi Wanpeng, > > sorry I could not answer before. > > We do not need to implement AutoHalt. It's a messy functionality and > the way it works is much simpler: on RSM the microcode reads AutoHALT's > bit 0 and... decrements RIP if it is 1. All you need to do however is > clear the activity state. Guests should expect anyway that "CLI;HLT" > can be interrupted by an NMI and follow it with a JMP. Thanks for pointing out. > > Second, I would prefer to implement at the same time MWAIT and PAUSE > passthrough, as in https://www.spinics.net/lists/kvm/msg159517.html: Understand. > >> The three capabilities are more or less all doing the same thing. >> Perhaps it would make some sense to only leave PAUSE spin loops in >> guest, but not HLT/MWAIT; but apart from that I think users would >> probably enable all of them. So I think we should put in the >> documentation that blindly passing the KVM_CHECK_EXTENSION result to >> KVM_ENABLE_CAP is a valid thing to do when vCPUs are associated to >> dedicated physical CPUs. >> >> Let's get rid of KVM_CAP_X86_GUEST_MWAIT altogether and >> add a new capability. But let's use just one. > > Thanks again for your work, and sorry for slightly contradicting Radim's > review. I've rebased and applied patch 2. No problem. You and Radim's review is always appreciated and helpful. Regards, Wanpeng Li
