From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
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@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
---
Documentation/virtual/kvm/api.txt | 26 ++++++++++++++++----------
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/svm.c | 2 +-
arch/x86/kvm/vmx.c | 9 +++++----
arch/x86/kvm/x86.c | 24 ++++++++++++++++++++----
arch/x86/kvm/x86.h | 10 +++++-----
include/uapi/linux/kvm.h | 2 +-
tools/include/uapi/linux/kvm.h | 2 +-
8 files changed, 51 insertions(+), 26 deletions(-)
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index da3b958..4df35c0 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1041,7 +1041,8 @@ On systems that do not support this ioctl, it always fails. On systems that
do support it, it only works for extensions that are supported for enablement.
To check if a capability can be enabled, the KVM_CHECK_EXTENSION ioctl should
-be used.
+be used. 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.
struct kvm_enable_cap {
/* in */
@@ -4358,6 +4359,20 @@ 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 exits 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 intercepts some instructions for improved latency in some
+workloads. Not enable KVM_FEATURE_PV_UNHALT if you block HLT.
+
8. Other capabilities.
----------------------
@@ -4470,15 +4485,6 @@ 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
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index df6720f..6bd754f 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -807,6 +807,8 @@ struct kvm_arch {
gpa_t wall_clock;
+ bool mwait_in_guest;
+
bool ept_identity_pagetable_done;
gpa_t ept_identity_map_addr;
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 312f33f..dff3a5d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1389,7 +1389,7 @@ 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);
}
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 2cdbea7..b551067 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3713,13 +3713,11 @@ 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;
@@ -5503,6 +5501,9 @@ 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;
}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5c93cbc..c1d9bbb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2780,9 +2780,15 @@ static int msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs __user *user_msrs,
return r;
}
+static inline bool kvm_mwait_can_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:
@@ -2838,8 +2844,9 @@ 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_mwait_can_in_guest())
+ r |= KVM_X86_DISABLE_EXITS_MWAIT;
break;
case KVM_CAP_X86_SMM:
/* SMBASE is usually relocated above 1M on modern chipsets,
@@ -2880,7 +2887,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = KVM_X2APIC_API_VALID_FLAGS;
break;
default:
- r = 0;
break;
}
return r;
@@ -4185,6 +4191,16 @@ 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_mwait_can_in_guest())
+ kvm->arch.mwait_in_guest = true;
+ r = 0;
+ break;
default:
r = -EINVAL;
break;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index b91215d..cd1215e 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -2,8 +2,6 @@
#ifndef ARCH_X86_KVM_X86_H
#define ARCH_X86_KVM_X86_H
-#include <asm/processor.h>
-#include <asm/mwait.h>
#include <linux/kvm_host.h>
#include <asm/pvclock.h>
#include "kvm_cache_regs.h"
@@ -264,10 +262,12 @@ static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
__rem; \
})
-static inline bool kvm_mwait_in_guest(void)
+#define KVM_X86_DISABLE_EXITS_MWAIT (1 << 0)
+#define KVM_X86_DISABLE_VALID_EXITS (KVM_X86_DISABLE_EXITS_MWAIT)
+
+static inline bool kvm_mwait_in_guest(struct kvm *kvm)
{
- return boot_cpu_has(X86_FEATURE_MWAIT) &&
- !boot_cpu_has_bug(X86_BUG_MONITOR);
+ return kvm->arch.mwait_in_guest;
}
#endif
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 088c2c9..1065006 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -929,7 +929,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_S390_GS 140
#define KVM_CAP_S390_AIS 141
#define KVM_CAP_SPAPR_TCE_VFIO 142
-#define KVM_CAP_X86_GUEST_MWAIT 143
+#define KVM_CAP_X86_DISABLE_EXITS 143
#define KVM_CAP_ARM_USER_IRQ 144
#define KVM_CAP_S390_CMMA_MIGRATION 145
#define KVM_CAP_PPC_FWNMI 146
diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h
index 8fb90a0..a81df22 100644
--- a/tools/include/uapi/linux/kvm.h
+++ b/tools/include/uapi/linux/kvm.h
@@ -924,7 +924,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_S390_GS 140
#define KVM_CAP_S390_AIS 141
#define KVM_CAP_SPAPR_TCE_VFIO 142
-#define KVM_CAP_X86_GUEST_MWAIT 143
+#define KVM_CAP_X86_DISABLE_EXITS 143
#define KVM_CAP_ARM_USER_IRQ 144
#define KVM_CAP_S390_CMMA_MIGRATION 145
#define KVM_CAP_PPC_FWNMI 146
--
2.7.4
