[PATCH v6 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

Tao Xu
2019-06-21T06:00:34Z

UMWAIT and TPAUSE instructions use IA32_UMWAIT_CONTROL at MSR index E1H
to determines the maximum time in TSC-quanta that the processor can reside
in either C0.1 or C0.2.

This patch emulates MSR IA32_UMWAIT_CONTROL in guest and differentiate
IA32_UMWAIT_CONTROL between host and guest. The variable
mwait_control_cached in arch/x86/power/umwait.c caches the MSR value, so
this patch uses it to avoid frequently rdmsr of IA32_UMWAIT_CONTROL.

Co-developed-by: Jingqi Liu <jingqi.liu@intel.com>
Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
Signed-off-by: Tao Xu <tao3.xu@intel.com>
---

Changes in v6:
add check msr_info->host_initiated in get/set msr(Xiaoyao)
restore the atomic_switch_umwait_control_msr()(Xiaoyao)
rebase the patch because the kernel dependcy patch updated to
v5: https://lkml.org/lkml/2019/6/19/972
---
arch/x86/kernel/cpu/umwait.c | 3 ++-
arch/x86/kvm/vmx/vmx.c | 33 +++++++++++++++++++++++++++++++++
arch/x86/kvm/vmx/vmx.h | 3 +++
arch/x86/kvm/x86.c | 1 +
4 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/umwait.c b/arch/x86/kernel/cpu/umwait.c
index 4b2aff7b2d4d..db5c193ef136 100644
--- a/arch/x86/kernel/cpu/umwait.c
+++ b/arch/x86/kernel/cpu/umwait.c
@@ -15,7 +15,8 @@
* MSR value. By default, umwait max time is 100000 in TSC-quanta and C0.2
* is enabled
*/
-static u32 umwait_control_cached = UMWAIT_CTRL_VAL(100000, UMWAIT_C02_ENABLED);
+u32 umwait_control_cached = UMWAIT_CTRL_VAL(100000, UMWAIT_C02_ENABLED);
+EXPORT_SYMBOL_GPL(umwait_control_cached);

/*
* Serialize access to umwait_control_cached and IA32_UMWAIT_CONTROL MSR
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b35bfac30a34..0d81cb9b96cf 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1679,6 +1679,13 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
#endif
case MSR_EFER:
return kvm_get_msr_common(vcpu, msr_info);
+ case MSR_IA32_UMWAIT_CONTROL:
+ if (!msr_info->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_WAITPKG))
+ return 1;
+
+ msr_info->data = vmx->msr_ia32_umwait_control;
+ break;
case MSR_IA32_SPEC_CTRL:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
@@ -1841,6 +1848,17 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return 1;
vmcs_write64(GUEST_BNDCFGS, data);
break;
+ case MSR_IA32_UMWAIT_CONTROL:
+ if (!msr_info->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_WAITPKG))
+ return 1;
+
+ /* The reserved bit IA32_UMWAIT_CONTROL[1] should be zero */
+ if (data & BIT_ULL(1))
+ return 1;
+
+ vmx->msr_ia32_umwait_control = data;
+ break;
case MSR_IA32_SPEC_CTRL:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
@@ -4126,6 +4144,8 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
vmx->rmode.vm86_active = 0;
vmx->spec_ctrl = 0;

+ vmx->msr_ia32_umwait_control = 0;
+
vcpu->arch.microcode_version = 0x100000000ULL;
vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
kvm_set_cr8(vcpu, 0);
@@ -6339,6 +6359,16 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
msrs[i].host, false);
}

+static void atomic_switch_umwait_control_msr(struct vcpu_vmx *vmx)
+{
+ if (vmx->msr_ia32_umwait_control != umwait_control_cached)
+ add_atomic_switch_msr(vmx, MSR_IA32_UMWAIT_CONTROL,
+ vmx->msr_ia32_umwait_control,
+ umwait_control_cached, false);
+ else
+ clear_atomic_switch_msr(vmx, MSR_IA32_UMWAIT_CONTROL);
+}
+
static void vmx_arm_hv_timer(struct vcpu_vmx *vmx, u32 val)
{
vmcs_write32(VMX_PREEMPTION_TIMER_VALUE, val);
@@ -6447,6 +6477,9 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)

atomic_switch_perf_msrs(vmx);

+ if (guest_cpuid_has(vcpu, X86_FEATURE_WAITPKG))
+ atomic_switch_umwait_control_msr(vmx);
+
vmx_update_hv_timer(vcpu);

/*
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 61128b48c503..8485bec7c38a 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -14,6 +14,8 @@
extern const u32 vmx_msr_index[];
extern u64 host_efer;

+extern u32 umwait_control_cached;
+
#define MSR_TYPE_R 1
#define MSR_TYPE_W 2
#define MSR_TYPE_RW 3
@@ -194,6 +196,7 @@ struct vcpu_vmx {
#endif

u64 spec_ctrl;
+ u64 msr_ia32_umwait_control;

u32 vm_entry_controls_shadow;
u32 vm_exit_controls_shadow;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 83aefd759846..4480de459bf4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1138,6 +1138,7 @@ static u32 msrs_to_save[] = {
MSR_IA32_RTIT_ADDR1_A, MSR_IA32_RTIT_ADDR1_B,
MSR_IA32_RTIT_ADDR2_A, MSR_IA32_RTIT_ADDR2_B,
MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
+ MSR_IA32_UMWAIT_CONTROL,
};

static unsigned num_msrs_to_save;
--
2.20.1