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Subject[PATCH v8 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL
Date
UMWAIT and TPAUSE instructions use 32bit 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/kernel/cpu/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 v8:
- Add an accessor to expose umwait_control_cached (Sean)
- Set msr_ia32_umwait_control in vcpu_vmx u32 and raise #GP when
[63:32] is set when rdmsr. (Sean)
---
arch/x86/kernel/cpu/umwait.c | 6 ++++++
arch/x86/kvm/vmx/vmx.c | 37 ++++++++++++++++++++++++++++++++++++
arch/x86/kvm/vmx/vmx.h | 9 +++++++++
arch/x86/kvm/x86.c | 1 +
4 files changed, 53 insertions(+)

diff --git a/arch/x86/kernel/cpu/umwait.c b/arch/x86/kernel/cpu/umwait.c
index 6a204e7336c1..e7344be24a74 100644
--- a/arch/x86/kernel/cpu/umwait.c
+++ b/arch/x86/kernel/cpu/umwait.c
@@ -17,6 +17,12 @@
*/
static u32 umwait_control_cached = UMWAIT_CTRL_VAL(100000, UMWAIT_C02_ENABLE);

+u32 get_umwait_control_msr(void)
+{
+ return umwait_control_cached;
+}
+EXPORT_SYMBOL_GPL(get_umwait_control_msr);
+
/*
* Serialize access to umwait_control_cached and IA32_UMWAIT_CONTROL MSR in
* the sysfs write functions.
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d4ee22ff7ccc..0224b087aad3 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1676,6 +1676,12 @@ 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 && !vmx_has_waitpkg(vmx))
+ 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))
@@ -1838,6 +1844,16 @@ 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 && !vmx_has_waitpkg(vmx))
+ return 1;
+
+ /* The reserved bit 1 and non-32 bit [63:32] should be zero */
+ if (data & (BIT_ULL(1) | GENMASK_ULL(63, 32)))
+ 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))
@@ -4137,6 +4153,8 @@ 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);
@@ -6350,6 +6368,23 @@ 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)
+{
+ u32 host_umwait_control;
+
+ if (!vmx_has_waitpkg(vmx))
+ return;
+
+ host_umwait_control = get_umwait_control_msr();
+
+ if (vmx->msr_ia32_umwait_control != host_umwait_control)
+ add_atomic_switch_msr(vmx, MSR_IA32_UMWAIT_CONTROL,
+ vmx->msr_ia32_umwait_control,
+ host_umwait_control, 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);
@@ -6458,6 +6493,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)

atomic_switch_perf_msrs(vmx);

+ 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..8e4869322eff 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 get_umwait_control_msr(void);
+
#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;
+ u32 msr_ia32_umwait_control;

u32 vm_entry_controls_shadow;
u32 vm_exit_controls_shadow;
@@ -523,6 +526,12 @@ static inline void decache_tsc_multiplier(struct vcpu_vmx *vmx)
vmcs_write64(TSC_MULTIPLIER, vmx->current_tsc_ratio);
}

+static inline bool vmx_has_waitpkg(struct vcpu_vmx *vmx)
+{
+ return vmx->secondary_exec_control &
+ SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE;
+}
+
void dump_vmcs(void);

#endif /* __KVM_X86_VMX_H */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 63bb1ee8258e..e914e4d03cce 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1136,6 +1136,7 @@ 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
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