On 07/05/20 16:44, Thomas Gleixner wrote: > Entering guest mode is more or less the same as returning to user > space. From an instrumentation point of view both leave kernel mode and the > transition to guest or user mode reenables interrupts on the host. In user > mode an interrupt is served directly and in guest mode it causes a VM exit > which then handles or reinjects the interrupt. > > The transition from guest mode or user mode to kernel mode disables > interrupts, which needs to be recorded in instrumentation to set the > correct state again. > > This is important for e.g. latency analysis because otherwise the execution > time in guest or user mode would be wrongly accounted as interrupt disabled > and could trigger false positives. > > Add hardirq tracing to guest enter/exit functions in the same way as it > is done in the user mode enter/exit code, respecting the RCU requirements. > > Signed-off-by: Thomas Gleixner <[email protected]> > Cc: Paolo Bonzini <[email protected]> > Cc: Sean Christopherson <[email protected]> > --- > V5: Adjust comments and changelog
Apart from the subject being svm and not vmx, it looks great. Thanks! Paolo > --- > arch/x86/kvm/vmx/vmx.c | 27 +++++++++++++++++++++++++-- > 1 file changed, 25 insertions(+), 2 deletions(-) > > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -6604,9 +6604,21 @@ static void vmx_vcpu_run(struct kvm_vcpu > x86_spec_ctrl_set_guest(vmx->spec_ctrl, 0); > > /* > - * Tell context tracking that this CPU is about to enter guest mode. > + * VMENTER enables interrupts (host state), but the kernel state is > + * interrupts disabled when this is invoked. Also tell RCU about > + * it. This is the same logic as for exit_to_user_mode(). > + * > + * This ensures that e.g. latency analysis on the host observes > + * guest mode as interrupt enabled. > + * > + * guest_enter_irqoff() informs context tracking about the > + * transition to guest mode and if enabled adjusts RCU state > + * accordingly. > */ > + trace_hardirqs_on_prepare(); > + lockdep_hardirqs_on_prepare(CALLER_ADDR0); > guest_enter_irqoff(); > + lockdep_hardirqs_on(CALLER_ADDR0); > > /* L1D Flush includes CPU buffer clear to mitigate MDS */ > if (static_branch_unlikely(&vmx_l1d_should_flush)) > @@ -6623,9 +6635,20 @@ static void vmx_vcpu_run(struct kvm_vcpu > vcpu->arch.cr2 = read_cr2(); > > /* > - * Tell context tracking that this CPU is back. > + * VMEXIT disables interrupts (host state), but tracing and lockdep > + * have them in state 'on' as recorded before entering guest mode. > + * Same as enter_from_user_mode(). > + * > + * guest_exit_irqoff() restores host context and reinstates RCU if > + * enabled and required. > + * > + * This needs to be done before the below as native_read_msr() > + * contains a tracepoint and x86_spec_ctrl_restore_host() calls > + * into world and some more. > */ > + lockdep_hardirqs_off(CALLER_ADDR0); > guest_exit_irqoff(); > + trace_hardirqs_off_prepare(); > > /* > * We do not use IBRS in the kernel. If this vCPU has used the >
