kvm: nVMX: Remove superfluous VMX instruction fault checks

According to the Intel SDM, "Certain exceptions have priority over VM
exits. These include invalid-opcode exceptions, faults based on
privilege level*, and general-protection exceptions that are based on
checking I/O permission bits in the task-state segment (TSS)."

There is no need to check for faulting conditions that the hardware
has already checked.

* These include faults generated by attempts to execute, in
  virtual-8086 mode, privileged instructions that are not recognized
  in that mode.

Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index b003b8d..75e6cc9 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -7052,34 +7052,24 @@ out_msr_bitmap:
 static int handle_vmon(struct kvm_vcpu *vcpu)
 {
        int ret;
-       struct kvm_segment cs;
        struct vcpu_vmx *vmx = to_vmx(vcpu);
        const u64 VMXON_NEEDED_FEATURES = FEATURE_CONTROL_LOCKED
                | FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX;
 
-       /* The Intel VMX Instruction Reference lists a bunch of bits that
-        * are prerequisite to running VMXON, most notably cr4.VMXE must be
-        * set to 1 (see vmx_set_cr4() for when we allow the guest to set this).
-        * Otherwise, we should fail with #UD. We test these now:
+       /*
+        * The Intel VMX Instruction Reference lists a bunch of bits that are
+        * prerequisite to running VMXON, most notably cr4.VMXE must be set to
+        * 1 (see vmx_set_cr4() for when we allow the guest to set this).
+        * Otherwise, we should fail with #UD.  But most faulting conditions
+        * have already been checked by hardware, prior to the VM-exit for
+        * VMXON.  We do test guest cr4.VMXE because processor CR4 always has
+        * that bit set to 1 in non-root mode.
         */
-       if (!kvm_read_cr4_bits(vcpu, X86_CR4_VMXE) ||
-           !kvm_read_cr0_bits(vcpu, X86_CR0_PE) ||
-           (vmx_get_rflags(vcpu) & X86_EFLAGS_VM)) {
-               kvm_queue_exception(vcpu, UD_VECTOR);
-               return 1;
-       }
-
-       vmx_get_segment(vcpu, &cs, VCPU_SREG_CS);
-       if (is_long_mode(vcpu) && !cs.l) {
+       if (!kvm_read_cr4_bits(vcpu, X86_CR4_VMXE)) {
                kvm_queue_exception(vcpu, UD_VECTOR);
                return 1;
        }
 
-       if (vmx_get_cpl(vcpu)) {
-               kvm_inject_gp(vcpu, 0);
-               return 1;
-       }
-
        if (vmx->nested.vmxon) {
                nested_vmx_failValid(vcpu, VMXERR_VMXON_IN_VMX_ROOT_OPERATION);
                return kvm_skip_emulated_instruction(vcpu);
@@ -7106,29 +7096,15 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
  * Intel's VMX Instruction Reference specifies a common set of prerequisites
  * for running VMX instructions (except VMXON, whose prerequisites are
  * slightly different). It also specifies what exception to inject otherwise.
+ * Note that many of these exceptions have priority over VM exits, so they
+ * don't have to be checked again here.
  */
 static int nested_vmx_check_permission(struct kvm_vcpu *vcpu)
 {
-       struct kvm_segment cs;
-       struct vcpu_vmx *vmx = to_vmx(vcpu);
-
-       if (!vmx->nested.vmxon) {
+       if (!to_vmx(vcpu)->nested.vmxon) {
                kvm_queue_exception(vcpu, UD_VECTOR);
                return 0;
        }
-
-       vmx_get_segment(vcpu, &cs, VCPU_SREG_CS);
-       if ((vmx_get_rflags(vcpu) & X86_EFLAGS_VM) ||
-           (is_long_mode(vcpu) && !cs.l)) {
-               kvm_queue_exception(vcpu, UD_VECTOR);
-               return 0;
-       }
-
-       if (vmx_get_cpl(vcpu)) {
-               kvm_inject_gp(vcpu, 0);
-               return 0;
-       }
-
        return 1;
 }
 
@@ -7472,7 +7448,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
                if (get_vmx_mem_address(vcpu, exit_qualification,
                                vmx_instruction_info, true, &gva))
                        return 1;
-               /* _system ok, as nested_vmx_check_permission verified cpl=0 */
+               /* _system ok, as hardware has verified cpl=0 */
                kvm_write_guest_virt_system(&vcpu->arch.emulate_ctxt, gva,
                             &field_value, (is_long_mode(vcpu) ? 8 : 4), NULL);
        }
@@ -7605,7 +7581,7 @@ static int handle_vmptrst(struct kvm_vcpu *vcpu)
        if (get_vmx_mem_address(vcpu, exit_qualification,
                        vmx_instruction_info, true, &vmcs_gva))
                return 1;
-       /* ok to use *_system, as nested_vmx_check_permission verified cpl=0 */
+       /* ok to use *_system, as hardware has verified cpl=0 */
        if (kvm_write_guest_virt_system(&vcpu->arch.emulate_ctxt, vmcs_gva,
                                 (void *)&to_vmx(vcpu)->nested.current_vmptr,
                                 sizeof(u64), &e)) {
@@ -7638,11 +7614,6 @@ static int handle_invept(struct kvm_vcpu *vcpu)
        if (!nested_vmx_check_permission(vcpu))
                return 1;
 
-       if (!kvm_read_cr0_bits(vcpu, X86_CR0_PE)) {
-               kvm_queue_exception(vcpu, UD_VECTOR);
-               return 1;
-       }
-
        vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
        type = kvm_register_readl(vcpu, (vmx_instruction_info >> 28) & 0xf);