linux-kernel - Re: [PATCH v19 085/130] KVM: TDX: Complete interrupts after tdexit

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Date: Mon, 17 Jun 2024 17:07:56 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Yuan Yao <yuan.yao@...ux.intel.com>, isaku.yamahata@...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
Subject: Re: [PATCH v19 085/130] KVM: TDX: Complete interrupts after tdexit



On 6/17/2024 4:07 PM, Yuan Yao wrote:
> On Mon, Feb 26, 2024 at 12:26:27AM -0800, isaku.yamahata@...el.com wrote:
>> From: Isaku Yamahata <isaku.yamahata@...el.com>
>>
>> This corresponds to VMX __vmx_complete_interrupts().  Because TDX
>> virtualize vAPIC, KVM only needs to care NMI injection.
>>
>> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
>> Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
>> Reviewed-by: Binbin Wu <binbin.wu@...ux.intel.com>
>> ---
>> v19:
>> - move tdvps_management_check() to this patch
>> - typo: complete -> Complete in short log
>> ---
>>   arch/x86/kvm/vmx/tdx.c | 10 ++++++++++
>>   arch/x86/kvm/vmx/tdx.h |  4 ++++
>>   2 files changed, 14 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
>> index 83dcaf5b6fbd..b8b168f74dfe 100644
>> --- a/arch/x86/kvm/vmx/tdx.c
>> +++ b/arch/x86/kvm/vmx/tdx.c
>> @@ -535,6 +535,14 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>   	 */
>>   }
>>
>> +static void tdx_complete_interrupts(struct kvm_vcpu *vcpu)
>> +{
>> +	/* Avoid costly SEAMCALL if no nmi was injected */
>> +	if (vcpu->arch.nmi_injected)
>> +		vcpu->arch.nmi_injected = td_management_read8(to_tdx(vcpu),
>> +							      TD_VCPU_PEND_NMI);
>> +}
> Looks this leads to NMI injection delay or even won't be
> reinjected if KVM_REQ_EVENT is not set on the target cpu
> when more than 1 NMIs are pending there.
>
> On normal VM, KVM uses NMI window vmexit for injection
> successful case to rasie the KVM_REQ_EVENT again for remain
> pending NMIs, see handle_nmi_window(). KVM also checks
> vectoring info after VMEXIT for case that the NMI is not
> injected successfully in this vmentry vmexit round, and
> raise KVM_REQ_EVENT to try again, see __vmx_complete_interrupts().
>
> In TDX, consider there's no way to get vectoring info or
> handle nmi window vmexit, below checking should cover both
> scenarios for NMI injection:
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index e9c9a185bb7b..9edf446acd3b 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -835,9 +835,12 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>   static void tdx_complete_interrupts(struct kvm_vcpu *vcpu)
>   {
>          /* Avoid costly SEAMCALL if no nmi was injected */
> -       if (vcpu->arch.nmi_injected)
> +       if (vcpu->arch.nmi_injected) {
>                  vcpu->arch.nmi_injected = td_management_read8(to_tdx(vcpu),
>                                                                TD_VCPU_PEND_NMI);
> +               if (vcpu->arch.nmi_injected || vcpu->arch.nmi_pending)
> +                       kvm_make_request(KVM_REQ_EVENT, vcpu);

For nmi_injected, it should be OK because TD_VCPU_PEND_NMI is still set.
But for nmi_pending, it should be checked and raise event.

I remember there was a discussion in the following link:
https://lore.kernel.org/kvm/20240402065254.GY2444378@ls.amr.corp.intel.com/
It said  tdx_vcpu_run() will ignore force_immediate_exit.
If force_immediate_exit is igored for TDX, then the nmi_pending handling 
could still be delayed if the previous NMI was injected successfully.


> +       }
>   }
>
>> +
>>   struct tdx_uret_msr {
>>   	u32 msr;
>>   	unsigned int slot;
>> @@ -663,6 +671,8 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
>>   	vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
>>   	trace_kvm_exit(vcpu, KVM_ISA_VMX);
>>
>> +	tdx_complete_interrupts(vcpu);
>> +
>>   	return EXIT_FASTPATH_NONE;
>>   }
>>
>> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
>> index 44eab734e702..0d8a98feb58e 100644
>> --- a/arch/x86/kvm/vmx/tdx.h
>> +++ b/arch/x86/kvm/vmx/tdx.h
>> @@ -142,6 +142,8 @@ static __always_inline void tdvps_vmcs_check(u32 field, u8 bits)
>>   			 "Invalid TD VMCS access for 16-bit field");
>>   }
>>
>> +static __always_inline void tdvps_management_check(u64 field, u8 bits) {}
>> +
>>   #define TDX_BUILD_TDVPS_ACCESSORS(bits, uclass, lclass)				\
>>   static __always_inline u##bits td_##lclass##_read##bits(struct vcpu_tdx *tdx,	\
>>   							u32 field)		\
>> @@ -200,6 +202,8 @@ TDX_BUILD_TDVPS_ACCESSORS(16, VMCS, vmcs);
>>   TDX_BUILD_TDVPS_ACCESSORS(32, VMCS, vmcs);
>>   TDX_BUILD_TDVPS_ACCESSORS(64, VMCS, vmcs);
>>
>> +TDX_BUILD_TDVPS_ACCESSORS(8, MANAGEMENT, management);
>> +
>>   static __always_inline u64 td_tdcs_exec_read64(struct kvm_tdx *kvm_tdx, u32 field)
>>   {
>>   	struct tdx_module_args out;
>> --
>> 2.25.1
>>
>>