Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754127AbdCIWgW (ORCPT ); Thu, 9 Mar 2017 17:36:22 -0500 Received: from mail.kernel.org ([198.145.29.136]:37280 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753578AbdCIWgT (ORCPT ); Thu, 9 Mar 2017 17:36:19 -0500 Date: Fri, 10 Mar 2017 00:29:31 +0200 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org Subject: [PATCH] kvm: better MWAIT emulation for guests Message-ID: <1489098555-23856-1-git-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Mailer: git-send-email 2.8.0.287.g0deeb61 X-Mutt-Fcc: =sent Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3356 Lines: 78 Some guests call mwait without checking the cpu flags. We currently emulate that as a NOP but on VMX we can do better: let guest stop the CPU until timer or IPI. CPU will be busy but that isn't any worse than a NOP emulation. Note that mwait within guests is not the same as on real hardware because you must halt if you want to go deep into sleep. Thus it isn't a good idea to use the regular MWAIT flag in CPUID for that. Add a flag in the hypervisor leaf instead. Signed-off-by: Michael S. Tsirkin --- Documentation/virtual/kvm/cpuid.txt | 3 +++ arch/x86/include/uapi/asm/kvm_para.h | 1 + arch/x86/kvm/cpuid.c | 3 +++ arch/x86/kvm/vmx.c | 4 ---- 4 files changed, 7 insertions(+), 4 deletions(-) diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt index 3c65feb..5caa234 100644 --- a/Documentation/virtual/kvm/cpuid.txt +++ b/Documentation/virtual/kvm/cpuid.txt @@ -54,6 +54,9 @@ KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit || || before enabling paravirtualized || || spinlock support. ------------------------------------------------------------------------------ +KVM_FEATURE_MWAIT || 8 || guest can use monitor/mwait + || || to halt the VCPU. +------------------------------------------------------------------------------ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side || || per-cpu warps are expected in || || kvmclock. diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h index cff0bb6..9cc77a7 100644 --- a/arch/x86/include/uapi/asm/kvm_para.h +++ b/arch/x86/include/uapi/asm/kvm_para.h @@ -24,6 +24,7 @@ #define KVM_FEATURE_STEAL_TIME 5 #define KVM_FEATURE_PV_EOI 6 #define KVM_FEATURE_PV_UNHALT 7 +#define KVM_FEATURE_MWAIT 8 /* The last 8 bits are used to indicate how to interpret the flags field * in pvclock structure. If no bits are set, all flags are ignored. diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index efde6cc..fe3d292 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -594,6 +594,9 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, if (sched_info_on()) entry->eax |= (1 << KVM_FEATURE_STEAL_TIME); + if (this_cpu_has(X86_FEATURE_MWAIT)) + entry->eax = (1 << KVM_FEATURE_MWAIT); + entry->ebx = 0; entry->ecx = 0; entry->edx = 0; diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 4bfe349..b167aba 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -3547,13 +3547,9 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf) CPU_BASED_USE_IO_BITMAPS | CPU_BASED_MOV_DR_EXITING | CPU_BASED_USE_TSC_OFFSETING | - CPU_BASED_MWAIT_EXITING | - CPU_BASED_MONITOR_EXITING | CPU_BASED_INVLPG_EXITING | CPU_BASED_RDPMC_EXITING; - printk(KERN_ERR "cleared CPU_BASED_MWAIT_EXITING + CPU_BASED_MONITOR_EXITING\n"); - opt = CPU_BASED_TPR_SHADOW | CPU_BASED_USE_MSR_BITMAPS | CPU_BASED_ACTIVATE_SECONDARY_CONTROLS; -- MST