Re: [PATCH v2 3/3] KVM: VMX: read idt_vectoring_info a bit earlier
On Thu, 2021-01-14 at 16:29 -0800, Sean Christopherson wrote:
> On Thu, Jan 14, 2021, Maxim Levitsky wrote:
> > This allows it to be printed correctly by the trace print
>
> It'd be helpful to explicitly say which tracepoint, and explain that the value
> is read by vmx_get_exit_info(). It's far from obvious how this gets consumed.
>
> > that follows.
> >
>
> Fixes: dcf068da7eb2 ("KVM: VMX: Introduce generic fastpath handler")
>
> > Signed-off-by: Maxim Levitsky
> > ---
> > arch/x86/kvm/vmx/vmx.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 2af05d3b05909..9b6e7dbf5e2bd 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -6771,6 +6771,8 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
> > }
> >
> > vmx->exit_reason = vmcs_read32(VM_EXIT_REASON);
> > + vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
>
> Hrm, it probably makes sense to either do the VMREAD conditionally, or to
> zero idt_vectoring_info in the vmx->fail path. I don't care about the cycles
> on VM-Exit consistency checks, just that this would hide that the field is
> valid
> if and only if VM-Enter fully succeeded. A third option would be to add a
> comment saying that it's unnecessary if VM-Enter failed, but faster in the
> common case to just do the VMREAD.
Allright, I will add this.
Best regards,
Maxim Levitsky
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 2af05d3b0590..3c172c05570a 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6774,13 +6774,15 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
> if (unlikely((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY))
> kvm_machine_check();
>
> + if (likely(!(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY)))
> + vmx->idt_vectoring_info =
> vmcs_read32(IDT_VECTORING_INFO_FIELD);
> +
> trace_kvm_exit(vmx->exit_reason, vcpu, KVM_ISA_VMX);
>
> if (unlikely(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
> return EXIT_FASTPATH_NONE;
>
> vmx->loaded_vmcs->launched = 1;
> - vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
>
> vmx_recover_nmi_blocking(vmx);
> vmx_complete_interrupts(vmx);
>
>
> > +
> > if (unlikely((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY))
> > kvm_machine_check();
> >
> > @@ -6780,7 +6782,6 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
> > return EXIT_FASTPATH_NONE;
> >
> > vmx->loaded_vmcs->launched = 1;
> > - vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
> >
> > vmx_recover_nmi_blocking(vmx);
> > vmx_complete_interrupts(vmx);
> > --
> > 2.26.2
> >
Re: [PATCH v2 3/3] KVM: VMX: read idt_vectoring_info a bit earlier
On Thu, Jan 14, 2021, Maxim Levitsky wrote:
> This allows it to be printed correctly by the trace print
It'd be helpful to explicitly say which tracepoint, and explain that the value
is read by vmx_get_exit_info(). It's far from obvious how this gets consumed.
> that follows.
>
Fixes: dcf068da7eb2 ("KVM: VMX: Introduce generic fastpath handler")
> Signed-off-by: Maxim Levitsky
> ---
> arch/x86/kvm/vmx/vmx.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 2af05d3b05909..9b6e7dbf5e2bd 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6771,6 +6771,8 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
> }
>
> vmx->exit_reason = vmcs_read32(VM_EXIT_REASON);
> + vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
Hrm, it probably makes sense to either do the VMREAD conditionally, or to
zero idt_vectoring_info in the vmx->fail path. I don't care about the cycles
on VM-Exit consistency checks, just that this would hide that the field is valid
if and only if VM-Enter fully succeeded. A third option would be to add a
comment saying that it's unnecessary if VM-Enter failed, but faster in the
common case to just do the VMREAD.
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 2af05d3b0590..3c172c05570a 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6774,13 +6774,15 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
if (unlikely((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY))
kvm_machine_check();
+ if (likely(!(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY)))
+ vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
+
trace_kvm_exit(vmx->exit_reason, vcpu, KVM_ISA_VMX);
if (unlikely(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
return EXIT_FASTPATH_NONE;
vmx->loaded_vmcs->launched = 1;
- vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
vmx_recover_nmi_blocking(vmx);
vmx_complete_interrupts(vmx);
> +
> if (unlikely((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY))
> kvm_machine_check();
>
> @@ -6780,7 +6782,6 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
> return EXIT_FASTPATH_NONE;
>
> vmx->loaded_vmcs->launched = 1;
> - vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
>
> vmx_recover_nmi_blocking(vmx);
> vmx_complete_interrupts(vmx);
> --
> 2.26.2
>
[PATCH v2 3/3] KVM: VMX: read idt_vectoring_info a bit earlier
This allows it to be printed correctly by the trace print that follows. Signed-off-by: Maxim Levitsky --- arch/x86/kvm/vmx/vmx.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 2af05d3b05909..9b6e7dbf5e2bd 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6771,6 +6771,8 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu) } vmx->exit_reason = vmcs_read32(VM_EXIT_REASON); + vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD); + if (unlikely((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY)) kvm_machine_check(); @@ -6780,7 +6782,6 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu) return EXIT_FASTPATH_NONE; vmx->loaded_vmcs->launched = 1; - vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD); vmx_recover_nmi_blocking(vmx); vmx_complete_interrupts(vmx); -- 2.26.2
