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

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Message-ID: <20240418000838.GA3596705@ls.amr.corp.intel.com>
Date: Wed, 17 Apr 2024 17:08:38 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: Isaku Yamahata <isaku.yamahata@...el.com>,
	Chao Gao <chao.gao@...el.com>, 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 Wed, Apr 17, 2024 at 11:05:05AM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> 
> 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();
>  }

You're correct. tdx_vcpu_enter_exit() handles EXIT_REASON_EXCEPTION_NMI for NMI,
and tdx_handle_exeption() ignores NMI case.

The commit message should be updated with tdx_vcpu_enter_exit().


> > > > 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?

Ok, tdx_handle_exception_nmi() is more consistent.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>