KVM: vmx: add support for emulating UMIP

UMIP can be emulated almost perfectly on Intel processor by enabling
descriptor-table exits.  SMSW does not cause a vmexit and hence it
cannot be changed into a #GP fault, but all in all it's the most
"innocuous" of the unprivileged instructions that UMIP blocks.

In fact, Linux is _also_ emulating SMSW instructions on behalf of the
program that executes them, because some 16-bit programs expect to use
SMSW to detect vm86 mode, so this is an even smaller issue.

Reviewed-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index b989cfe412b13b6aaf656e34c7b3ce8fe394d94f..ebd50de981ee67105b937b2b7c1324d8d9579911 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3662,6 +3662,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
                        SECONDARY_EXEC_ENABLE_EPT |
                        SECONDARY_EXEC_UNRESTRICTED_GUEST |
                        SECONDARY_EXEC_PAUSE_LOOP_EXITING |
+                       SECONDARY_EXEC_DESC |
                        SECONDARY_EXEC_RDTSCP |
                        SECONDARY_EXEC_ENABLE_INVPCID |
                        SECONDARY_EXEC_APIC_REGISTER_VIRT |
@@ -4369,6 +4370,14 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
                (to_vmx(vcpu)->rmode.vm86_active ?
                 KVM_RMODE_VM_CR4_ALWAYS_ON : KVM_PMODE_VM_CR4_ALWAYS_ON);
 
+       if ((cr4 & X86_CR4_UMIP) && !boot_cpu_has(X86_FEATURE_UMIP)) {
+               vmcs_set_bits(SECONDARY_VM_EXEC_CONTROL,
+                             SECONDARY_EXEC_DESC);
+               hw_cr4 &= ~X86_CR4_UMIP;
+       } else
+               vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL,
+                               SECONDARY_EXEC_DESC);
+
        if (cr4 & X86_CR4_VMXE) {
                /*
                 * To use VMXON (and later other VMX instructions), a guest
@@ -5308,6 +5317,7 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
        struct kvm_vcpu *vcpu = &vmx->vcpu;
 
        u32 exec_control = vmcs_config.cpu_based_2nd_exec_ctrl;
+
        if (!cpu_need_virtualize_apic_accesses(vcpu))
                exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
        if (vmx->vpid == 0)
@@ -5326,6 +5336,11 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
                exec_control &= ~(SECONDARY_EXEC_APIC_REGISTER_VIRT |
                                  SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY);
        exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE;
+
+       /* SECONDARY_EXEC_DESC is enabled/disabled on writes to CR4.UMIP,
+        * in vmx_set_cr4.  */
+       exec_control &= ~SECONDARY_EXEC_DESC;
+
        /* SECONDARY_EXEC_SHADOW_VMCS is enabled when L1 executes VMPTRLD
           (handle_vmptrld).
           We can NOT enable shadow_vmcs here because we don't have yet
@@ -6101,6 +6116,12 @@ static int handle_set_cr4(struct kvm_vcpu *vcpu, unsigned long val)
                return kvm_set_cr4(vcpu, val);
 }
 
+static int handle_desc(struct kvm_vcpu *vcpu)
+{
+       WARN_ON(!(vcpu->arch.cr4 & X86_CR4_UMIP));
+       return emulate_instruction(vcpu, 0) == EMULATE_DONE;
+}
+
 static int handle_cr(struct kvm_vcpu *vcpu)
 {
        unsigned long exit_qualification, val;
@@ -8193,6 +8214,8 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
        [EXIT_REASON_XSETBV]                  = handle_xsetbv,
        [EXIT_REASON_TASK_SWITCH]             = handle_task_switch,
        [EXIT_REASON_MCE_DURING_VMENTRY]      = handle_machine_check,
+       [EXIT_REASON_GDTR_IDTR]               = handle_desc,
+       [EXIT_REASON_LDTR_TR]                 = handle_desc,
        [EXIT_REASON_EPT_VIOLATION]           = handle_ept_violation,
        [EXIT_REASON_EPT_MISCONFIG]           = handle_ept_misconfig,
        [EXIT_REASON_PAUSE_INSTRUCTION]       = handle_pause,
@@ -9157,7 +9180,8 @@ static bool vmx_xsaves_supported(void)
 
 static bool vmx_umip_emulated(void)
 {
-       return false;
+       return vmcs_config.cpu_based_2nd_exec_ctrl &
+               SECONDARY_EXEC_DESC;
 }
 
 static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
@@ -9755,7 +9779,8 @@ static void vmcs_set_secondary_exec_control(u32 new_ctl)
        u32 mask =
                SECONDARY_EXEC_SHADOW_VMCS |
                SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
-               SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
+               SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
+               SECONDARY_EXEC_DESC;
 
        u32 cur_ctl = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);