Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 4d5422ce authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
Browse files

KVM: X86: Provide a capability to disable MWAIT intercepts 



Allowing a guest to execute MWAIT without interception enables a guest
to put a (physical) CPU into a power saving state, where it takes
longer to return from than what may be desired by the host.

Don't give a guest that power over a host by default. (Especially,
since nothing prevents a guest from using MWAIT even when it is not
advertised via CPUID.)

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Jan H. Schönherr <jschoenh@amazon.de>
Signed-off-by: default avatarWanpeng Li <wanpengli@tencent.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 4956aa3b

Documentation/virtual/kvm/api.txt

+18 −9
Original line number Diff line number Diff line
@@ -4358,6 +4358,24 @@ enables QEMU to build error log and branch to guest kernel registered 
machine check handling routine. Without this capability KVM will

branch to guests' 0x200 interrupt vector.



7.13 KVM_CAP_X86_DISABLE_EXITS



Architectures: x86

Parameters: args[0] defines which exits are disabled

Returns: 0 on success, -EINVAL when args[0] contains invalid exits



Valid bits in args[0] are



#define KVM_X86_DISABLE_EXITS_MWAIT            (1 << 0)



Enabling this capability on a VM provides userspace with a way to no

longer intercept some instructions for improved latency in some

workloads, and is suggested when vCPUs are associated to dedicated

physical CPUs.  More bits can be added in the future; userspace can

just pass the KVM_CHECK_EXTENSION result to KVM_ENABLE_CAP to disable

all such vmexits.





8. Other capabilities.

----------------------
@@ -4470,15 +4488,6 @@ reserved. 
    Both registers and addresses are 64-bits wide.

    It will be possible to run 64-bit or 32-bit guest code.



8.8 KVM_CAP_X86_GUEST_MWAIT



Architectures: x86



This capability indicates that guest using memory monotoring instructions

(MWAIT/MWAITX) to stop the virtual CPU will not cause a VM exit.  As such time

spent while virtual CPU is halted in this way will then be accounted for as

guest running time on the host (as opposed to e.g. HLT).



8.9 KVM_CAP_ARM_USER_IRQ



Architectures: arm, arm64

arch/x86/include/asm/kvm_host.h

+2 −0
Original line number Diff line number Diff line
@@ -811,6 +811,8 @@ struct kvm_arch { 


	gpa_t wall_clock;



	bool mwait_in_guest;



	bool ept_identity_pagetable_done;

	gpa_t ept_identity_map_addr;

arch/x86/kvm/svm.c

+1 −1
Original line number Diff line number Diff line
@@ -1398,7 +1398,7 @@ static void init_vmcb(struct vcpu_svm *svm) 
	set_intercept(svm, INTERCEPT_XSETBV);

	set_intercept(svm, INTERCEPT_RSM);



	if (!kvm_mwait_in_guest()) {

	if (!kvm_mwait_in_guest(svm->vcpu.kvm)) {

		set_intercept(svm, INTERCEPT_MONITOR);

		set_intercept(svm, INTERCEPT_MWAIT);

	}

arch/x86/kvm/vmx.c

+5 −4
Original line number Diff line number Diff line
@@ -3746,13 +3746,11 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf) 
	      CPU_BASED_UNCOND_IO_EXITING |

	      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;



	if (!kvm_mwait_in_guest())

		min |= CPU_BASED_MWAIT_EXITING |

			CPU_BASED_MONITOR_EXITING;



	opt = CPU_BASED_TPR_SHADOW |

	      CPU_BASED_USE_MSR_BITMAPS |

	      CPU_BASED_ACTIVATE_SECONDARY_CONTROLS;
@@ -5544,6 +5542,9 @@ static u32 vmx_exec_control(struct vcpu_vmx *vmx) 
		exec_control |= CPU_BASED_CR3_STORE_EXITING |

				CPU_BASED_CR3_LOAD_EXITING  |

				CPU_BASED_INVLPG_EXITING;

	if (kvm_mwait_in_guest(vmx->vcpu.kvm))

		exec_control &= ~(CPU_BASED_MWAIT_EXITING |

				CPU_BASED_MONITOR_EXITING);

	return exec_control;

}

arch/x86/kvm/x86.c

+20 −4
Original line number Diff line number Diff line
@@ -2813,9 +2813,15 @@ static int msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs __user *user_msrs, 
	return r;

}



static inline bool kvm_can_mwait_in_guest(void)

{

	return boot_cpu_has(X86_FEATURE_MWAIT) &&

		!boot_cpu_has_bug(X86_BUG_MONITOR);

}



int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)

{

	int r;

	int r = 0;



	switch (ext) {

	case KVM_CAP_IRQCHIP:
@@ -2871,8 +2877,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) 
	case KVM_CAP_ADJUST_CLOCK:

		r = KVM_CLOCK_TSC_STABLE;

		break;

	case KVM_CAP_X86_GUEST_MWAIT:

		r = kvm_mwait_in_guest();

	case KVM_CAP_X86_DISABLE_EXITS:

		if(kvm_can_mwait_in_guest())

			r |= KVM_X86_DISABLE_EXITS_MWAIT;

		break;

	case KVM_CAP_X86_SMM:

		/* SMBASE is usually relocated above 1M on modern chipsets,
@@ -2913,7 +2920,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) 
		r = KVM_X2APIC_API_VALID_FLAGS;

		break;

	default:

		r = 0;

		break;

	}

	return r;
@@ -4218,6 +4224,16 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, 


		r = 0;

		break;

	case KVM_CAP_X86_DISABLE_EXITS:

		r = -EINVAL;

		if (cap->args[0] & ~KVM_X86_DISABLE_VALID_EXITS)

			break;



		if ((cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT) &&

			kvm_can_mwait_in_guest())

			kvm->arch.mwait_in_guest = true;

		r = 0;

		break;

	default:

		r = -EINVAL;

		break;