| Message ID | 20220310111354.504565-1-zhenzhong.duan@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: Remove redundant vm_entry_controls_clearbit() call | expand |
On Thu, Mar 10, 2022, Zhenzhong Duan wrote: > When emulating exit from long mode, EFER_LMA is cleared which lead to > efer writing emulation, which will unset VM_ENTRY_IA32E_MODE control > bit as requested by SDM. So no need to unset VM_ENTRY_IA32E_MODE again > in exit_lmode() explicitly. > > In fact benefited from shadow controls mechanism, this change doesn't > eliminate vmread or vmwrite. > > Opportunistically remove unnecessory assignment to uret MSR data field > as vmx_setup_uret_msrs() will do the same thing. This needs to be a separate patch, it's much more subtle than "xyz will do the same thing". update_transition_efer() doesn't unconditionally set uret->data, which on the surface makes this look suspect, but it's safe because uret->data is consumed if and only if uret->load_into_hardware is true, and it's (a) set to false if uret->data isn't updated and (b) uret->data is guaranteed to be updated before it's set to true. > In case EFER isn't supported by hardware, long mode isn't supported, > so this will no break. > > > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com> > --- > arch/x86/kvm/vmx/vmx.c | 8 ++------ > 1 file changed, 2 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index b730d799c26e..b04588dc7faa 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -2878,14 +2878,11 @@ int vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer) > return 0; > > vcpu->arch.efer = efer; > - if (efer & EFER_LMA) { > + if (efer & EFER_LMA) > vm_entry_controls_setbit(to_vmx(vcpu), VM_ENTRY_IA32E_MODE); > - msr->data = efer; > - } else { > + else > vm_entry_controls_clearbit(to_vmx(vcpu), VM_ENTRY_IA32E_MODE); > > - msr->data = efer & ~EFER_LME; > - } While you're doing opportunistic cleanups, drop the local "msr" and use "vmx" directly instead of redoing to_vmx(), i.e. this int vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer) { struct vcpu_vmx *vmx = to_vmx(vcpu); /* Nothing to do if hardware doesn't support EFER. */ if (!vmx_find_uret_msr(vmx, MSR_EFER)) return 0; vcpu->arch.efer = efer; if (efer & EFER_LMA) vm_entry_controls_setbit(vmx, VM_ENTRY_IA32E_MODE); else vm_entry_controls_clearbit(vmx, VM_ENTRY_IA32E_MODE); vmx_setup_uret_msrs(vmx); return 0; }
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index b730d799c26e..b04588dc7faa 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -2878,14 +2878,11 @@ int vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer) return 0; vcpu->arch.efer = efer; - if (efer & EFER_LMA) { + if (efer & EFER_LMA) vm_entry_controls_setbit(to_vmx(vcpu), VM_ENTRY_IA32E_MODE); - msr->data = efer; - } else { + else vm_entry_controls_clearbit(to_vmx(vcpu), VM_ENTRY_IA32E_MODE); - msr->data = efer & ~EFER_LME; - } vmx_setup_uret_msrs(vmx); return 0; } @@ -2911,7 +2908,6 @@ static void enter_lmode(struct kvm_vcpu *vcpu) static void exit_lmode(struct kvm_vcpu *vcpu) { - vm_entry_controls_clearbit(to_vmx(vcpu), VM_ENTRY_IA32E_MODE); vmx_set_efer(vcpu, vcpu->arch.efer & ~EFER_LMA); }
When emulating exit from long mode, EFER_LMA is cleared which lead to efer writing emulation, which will unset VM_ENTRY_IA32E_MODE control bit as requested by SDM. So no need to unset VM_ENTRY_IA32E_MODE again in exit_lmode() explicitly. In fact benefited from shadow controls mechanism, this change doesn't eliminate vmread or vmwrite. Opportunistically remove unnecessory assignment to uret MSR data field as vmx_setup_uret_msrs() will do the same thing. In case EFER isn't supported by hardware, long mode isn't supported, so this will no break. Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com> --- arch/x86/kvm/vmx/vmx.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)