Re: [PATCH v7 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

[Tao Xu]

On 7/12/2019 11:52 PM, Sean Christopherson wrote:
On Fri, Jul 12, 2019 at 04:29:06PM +0800, Tao Xu wrote:
diff --git a/arch/x86/kernel/cpu/umwait.c b/arch/x86/kernel/cpu/umwait.c
index 6a204e7336c1..631152a67c6e 100644
--- a/arch/x86/kernel/cpu/umwait.c
+++ b/arch/x86/kernel/cpu/umwait.c
@@ -15,7 +15,8 @@
   * Cache IA32_UMWAIT_CONTROL MSR. This is a systemwide control. 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_ENABLE);
+u32 umwait_control_cached = UMWAIT_CTRL_VAL(100000, UMWAIT_C02_ENABLE);
+EXPORT_SYMBOL_GPL(umwait_control_cached);

It'd probably be better to add an accessor to expose umwait_control_cached
given that umwait.c is using {READ,WRITE}_ONCE() and there shouldn't be a
need to write it outside of umwait.c.


OKay

  /*
   * Serialize access to umwait_control_cached and IA32_UMWAIT_CONTROL MSR in
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f411c9ae5589..0787f140d155 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 IA32_UMWAIT_CONTROL[1] should be zero */
+               if (data & BIT_ULL(1))
+                       return 1;
+
+               vmx->msr_ia32_umwait_control = data;

The SDM only defines bits 31:0, and the kernel uses a u32 to cache its
value.  I assume bits 63:32 are reserved?  I'm guessing we also need an
SDM update...


The SDM define IA32_UMWAIT_CONTROL is a 32bit MSR. So need me to set 
63:32 reserved?

+               break;
        case MSR_IA32_SPEC_CTRL:
                if (!msr_info->host_initiated &&
                    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
@@ -4139,6 +4155,8 @@ 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);
@@ -6352,6 +6370,19 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
                                        msrs[i].host, false);
  }