RE: [PATCH v5 34/34] KVM: x86/vmx: execute "int $2" to handle NMI in NMI caused VM exits when FRED is enabled

Li, Xin3
2023-03-07T22:01:17Z

> Execute "int $2" to handle NMI in NMI caused VM exits when FRED is enabled.
>
> Like IRET for IDT, ERETS/ERETU are required to end the NMI handler for FRED
> to unblock NMI ASAP (w/ bit 28 of CS set). And there are 2 approaches to
> invoke the FRED NMI handler:
> 1) execute "int $2", let the h/w do the job.
> 2) create a FRED NMI stack frame on the current kernel stack with ASM,
> and then jump to fred_entrypoint_kernel in arch/x86/entry/entry_64_fred.S.
>
> 1) is preferred as we want less ASM.
>
> Tested-by: Shan Kang <shan.kang@intel.com>
> Signed-off-by: Xin Li <xin3.li@intel.com>
> ---
>
> Changes since v4:
> *) Do NOT use the term "injection", which in the KVM context means to
> reinject an event into the guest (Sean Christopherson).
> *) Add the explanation of why to execute "int $2" to invoke the NMI handler
> in NMI caused VM exits (Sean Christopherson).

Sean,

Do you have any further issue with the last 2 VMX patches?

If not, would you ack them?

Thanks!
Xin

> ---
> arch/x86/kvm/vmx/vmx.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 3ebeaab34b2e..4f12ead2266b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7229,7 +7229,16 @@ static noinstr void vmx_vcpu_enter_exit(struct
> kvm_vcpu *vcpu,
> if ((u16)vmx->exit_reason.basic == EXIT_REASON_EXCEPTION_NMI &&
> is_nmi(vmx_get_intr_info(vcpu))) {
> kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
> - vmx_do_nmi_irqoff();
> + /*
> + * Like IRET for IDT, ERETS/ERETU are required to end the NMI
> + * handler for FRED to unblock NMI ASAP (w/ bit 28 of CS set).
> + *
> + * Invoke the FRED NMI handler through executing "int $2".
> + */
> + if (cpu_feature_enabled(X86_FEATURE_FRED))
> + asm volatile("int $2");
> + else
> + vmx_do_nmi_irqoff();
> kvm_after_interrupt(vcpu);
> }
>
> --
> 2.34.1