Messages in this thread | | | Subject | Re: [PATCH v2 1/3] KVM: x86: add support for user wait instructions | From | Tao Xu <> | Date | Tue, 28 May 2019 15:19:30 +0800 |
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On 28/05/2019 14:11, Wanpeng Li wrote: > On Tue, 28 May 2019 at 13:16, Tao Xu <tao3.xu@intel.com> wrote: >> >> >> On 27/05/2019 18:30, Peter Zijlstra wrote: >>> On Fri, May 24, 2019 at 03:56:35PM +0800, Tao Xu wrote: >>>> This patch adds support for UMONITOR, UMWAIT and TPAUSE instructions >>>> in kvm, and by default dont't expose it to kvm and provide a capability >>>> to enable it. >>> >>> I'm thinking this should be conditional on the guest being a 1:1 guest, >>> and I also seem to remember we have bits for that already -- they were >>> used to disable paravirt spinlocks for example. >>> >> >> Hi Peter, >> >> I am wondering if "1:1 guest" means different guests in the same host >> should have different settings on user wait instructions? >> >> User wait instructions(UMONITOR, UMWAIT and TPAUSE) can use in guest >> only when the VMCS Secondary Processor-Based VM-Execution Control bit 26 >> is 1, otherwise any execution of TPAUSE, UMONITOR, or UMWAIT causes a #UD. >> >> So with a capability to enable it, we use qemu kvm_vm_ioctl_enable_cap() >> to enable it. The qemu link is blew: >> https://lists.gnu.org/archive/html/qemu-devel/2019-05/msg05810.html >> >> By using different QEMU parameters, different guests in the same host >> would have different features with or without user wait instructions. >> >> About "disable paravirt spinlocks" case, I am wondering if it uses > > Please refer to a4429e53c9 (KVM: Introduce paravirtualization hints > and KVM_HINTS_DEDICATED) and b2798ba0b87 (KVM: X86: Choose qspinlock > when dedicated physical CPUs are available) Hi Wanpeng,
Thank you! This information really helped me. After I read the code in KVM/QEMU, I was wondering that with qemu command-line "-cpu host,+kvm-hint-dedicated", then in KVM, "kvm_hint_has_feature(KVM_HINTS_DEDICATED)" will be true, am I right?
Tao
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