On Thu, Jun 06, 2019 at 07:24:38PM +0200, Paolo Bonzini wrote: > On 07/05/19 21:18, Sean Christopherson wrote: > > Pin controls doesn't affect dirty logic, e.g. the preemption timer value > > is loaded from vmcs12 even if vmcs12 is "clean", i.e. there is no need > > to mark vmcs12 dirty when L1 writes pin controls. > > > > KVM currently toggles the VMX_PREEMPTION_TIMER control flag when it > > disables or enables the timer. The VMWRITE to toggle the flag can be > > responsible for a large percentage of vmcs12 dirtying when running KVM > > as L1 (depending on the behavior of L2). > > > > Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> > > I think either we wait for patch 13 to get in the wild so that > VMX_PREEMPTION_TIMER writes do not become so frequent, or we can do > something like I'd prefer to get something in now. I assume a fair number of users will be running current/older versions of KVM as L1 for years to come. I have no objection to shadowing pin controls. I opted for the cheesy approach because I couldn't provide numbers that actually showed a performance improvement by shadowing. > --------- 8< ------------ > From: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Subject: [PATCH] KVM: nVMX: shadow pin based execution controls > > The VMX_PREEMPTION_TIMER flag may be toggled frequently, though not > *very* frequently. Since it does not affect KVM's dirty logic, e.g. > the preemption timer value is loaded from vmcs12 even if vmcs12 is > "clean", there is no need to mark vmcs12 dirty when L1 writes pin > controls, and shadowing the field achieves that. > > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > > diff --git a/arch/x86/kvm/vmx/vmcs_shadow_fields.h > b/arch/x86/kvm/vmx/vmcs_shadow_fields.h > index 4cea018ba285..eb1ecd16fd22 100644 > --- a/arch/x86/kvm/vmx/vmcs_shadow_fields.h > +++ b/arch/x86/kvm/vmx/vmcs_shadow_fields.h > @@ -47,6 +47,7 @@ > SHADOW_FIELD_RO(GUEST_CS_AR_BYTES, guest_cs_ar_bytes) > SHADOW_FIELD_RO(GUEST_SS_AR_BYTES, guest_ss_ar_bytes) > SHADOW_FIELD_RW(CPU_BASED_VM_EXEC_CONTROL, cpu_based_vm_exec_control) > +SHADOW_FIELD_RW(PIN_BASED_VM_EXEC_CONTROL, pin_based_vm_exec_control) > SHADOW_FIELD_RW(EXCEPTION_BITMAP, exception_bitmap) > SHADOW_FIELD_RW(VM_ENTRY_EXCEPTION_ERROR_CODE, > vm_entry_exception_error_code) > SHADOW_FIELD_RW(VM_ENTRY_INTR_INFO_FIELD, vm_entry_intr_info_field)
