linux-kernel - Re: [PATCH v19 102/130] KVM: TDX: handle EXCEPTION_NMI and EXTERNAL

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Date: Wed, 17 Apr 2024 11:05:05 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Isaku Yamahata <isaku.yamahata@...el.com>, Chao Gao <chao.gao@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
 isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 102/130] KVM: TDX: handle EXCEPTION_NMI and
 EXTERNAL_INTERRUPT



On 4/4/2024 2:51 AM, Isaku Yamahata wrote:
> On Mon, Apr 01, 2024 at 04:22:00PM +0800,
> Chao Gao <chao.gao@...el.com> wrote:
>
>> On Mon, Feb 26, 2024 at 12:26:44AM -0800, isaku.yamahata@...el.com wrote:
>>> From: Isaku Yamahata <isaku.yamahata@...el.com>
>>>
>>> Because guest TD state is protected, exceptions in guest TDs can't be
>>> intercepted.  TDX VMM doesn't need to handle exceptions.
>>> tdx_handle_exit_irqoff() handles NMI and machine check.  Ignore NMI and
>> tdx_handle_exit_irqoff() doesn't handle NMIs.
> Will it to tdx_handle_exception().

I don't get  why tdx_handle_exception()?

NMI is handled in tdx_vcpu_enter_exit() prior to leaving the safety of 
noinstr, according to patch 098.
https://lore.kernel.org/kvm/88920c598dcb55c15219642f27d0781af6d0c044.1708933498.git.isaku.yamahata@intel.com/

@@ -837,6 +857,12 @@ static noinstr void tdx_vcpu_enter_exit(struct 
vcpu_tdx *tdx)
      WARN_ON_ONCE(!kvm_rebooting &&
               (tdx->exit_reason.full & TDX_SW_ERROR) == TDX_SW_ERROR);

+    if ((u16)tdx->exit_reason.basic == EXIT_REASON_EXCEPTION_NMI &&
+        is_nmi(tdexit_intr_info(vcpu))) {
+        kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
+        vmx_do_nmi_irqoff();
+        kvm_after_interrupt(vcpu);
+    }
      guest_state_exit_irqoff();
  }

>
>
>>> machine check and continue guest TD execution.
>>>
>>> For external interrupt, increment stats same to the VMX case.
>>>
>>> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
>>> Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
>>> ---
>>> arch/x86/kvm/vmx/tdx.c | 23 +++++++++++++++++++++++
>>> 1 file changed, 23 insertions(+)
>>>
>>> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
>>> index 0db80fa020d2..bdd74682b474 100644
>>> --- a/arch/x86/kvm/vmx/tdx.c
>>> +++ b/arch/x86/kvm/vmx/tdx.c
>>> @@ -918,6 +918,25 @@ void tdx_handle_exit_irqoff(struct kvm_vcpu *vcpu)
>>> 		vmx_handle_exception_irqoff(vcpu, tdexit_intr_info(vcpu));
>>> }
>>>
>>> +static int tdx_handle_exception(struct kvm_vcpu *vcpu)

Should this function be named as tdx_handle_exception_nmi() since it's 
checking nmi as well?

>>> +{
>>> +	u32 intr_info = tdexit_intr_info(vcpu);
>>> +
>>> +	if (is_nmi(intr_info) || is_machine_check(intr_info))
>>> +		return 1;
>>