From: Tao Xu <tao3.xu@intel.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Radim Krcmar <rkrcmar@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
the arch/x86 maintainers <x86@kernel.org>,
kvm <kvm@vger.kernel.org>,
linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
jingqi.liu@intel.com
Subject: Re: [PATCH v2 1/3] KVM: x86: add support for user wait instructions
Date: Tue, 28 May 2019 15:19:30 +0800 [thread overview]
Message-ID: <072dd34e-0361-5a06-4d0b-d04e8150a3bb@intel.com> (raw)
In-Reply-To: <CANRm+CwnJoj0EwWoFC44SXVUTLdE+iFGovaMr4Yf=OzbaW36sA@mail.gmail.com>
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
next prev parent reply other threads:[~2019-05-28 7:21 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-24 7:56 [PATCH v2 0/3] KVM: x86: Enable user wait instructions Tao Xu
2019-05-24 7:56 ` [PATCH v2 1/3] KVM: x86: add support for " Tao Xu
2019-05-27 10:30 ` Peter Zijlstra
2019-05-28 5:11 ` Tao Xu
2019-05-28 6:11 ` Wanpeng Li
2019-05-28 7:19 ` Tao Xu [this message]
2019-05-29 1:26 ` Paolo Bonzini
2019-05-29 1:25 ` Paolo Bonzini
2019-05-29 1:24 ` Paolo Bonzini
2019-05-29 2:05 ` Tao Xu
2019-05-29 2:38 ` Paolo Bonzini
2019-05-29 3:12 ` Tao Xu
2019-05-24 7:56 ` [PATCH v2 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL Tao Xu
2019-05-29 1:29 ` Paolo Bonzini
2019-05-29 1:38 ` Tao Xu
2019-05-24 7:56 ` [PATCH v2 3/3] KVM: vmx: handle vm-exit for UMWAIT and TPAUSE Tao Xu
2019-05-29 1:28 ` Paolo Bonzini
2019-05-29 2:25 ` Tao Xu
2019-05-29 2:39 ` Paolo Bonzini
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