Re: [PATCH v5 6/8] KVM: VMX: enable IPI virtualization

[Zeng Guang <guang.zeng@intel.com>]

On 1/14/2022 5:47 AM, Sean Christopherson wrote:
> On Fri, Dec 31, 2021, Zeng Guang wrote:
>> +/* Tertiary Processor-Based VM-Execution Controls, word 3 */
>> +#define VMX_FEATURE_IPI_VIRT		(3*32 +  4) /* "" Enable IPI virtualization */
>>   #endif /* _ASM_X86_VMXFEATURES_H */
>> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
>> index 38d414f64e61..78b0525dd991 100644
>> --- a/arch/x86/kvm/vmx/capabilities.h
>> +++ b/arch/x86/kvm/vmx/capabilities.h
>> @@ -12,6 +12,7 @@ extern bool __read_mostly enable_ept;
>>   extern bool __read_mostly enable_unrestricted_guest;
>>   extern bool __read_mostly enable_ept_ad_bits;
>>   extern bool __read_mostly enable_pml;
>> +extern bool __read_mostly enable_ipiv;
>>   extern int __read_mostly pt_mode;
>>   
>>   #define PT_MODE_SYSTEM		0
>> @@ -283,6 +284,12 @@ static inline bool cpu_has_vmx_apicv(void)
>>   		cpu_has_vmx_posted_intr();
>>   }
>>   
>> +static inline bool cpu_has_vmx_ipiv(void)
>> +{
>> +	return vmcs_config.cpu_based_3rd_exec_ctrl &
>> +		TERTIARY_EXEC_IPI_VIRT;
> Unnecessary newline, that fits on a single line.

OK.

>> +}
>> +
>>   static inline bool cpu_has_vmx_flexpriority(void)
>>   {
>>   	return cpu_has_vmx_tpr_shadow() &&
>> diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
>> index 1c94783b5a54..bd9c9a89726a 100644
>> --- a/arch/x86/kvm/vmx/posted_intr.c
>> +++ b/arch/x86/kvm/vmx/posted_intr.c
>> @@ -85,11 +85,16 @@ static bool vmx_can_use_vtd_pi(struct kvm *kvm)
>>   		irq_remapping_cap(IRQ_POSTING_CAP);
>>   }
>>   
>> +static bool vmx_can_use_ipiv_pi(struct kvm *kvm)
>> +{
>> +	return irqchip_in_kernel(kvm) && enable_apicv && enable_ipiv;
> enable_ipiv should be cleared if !enable_apicv, i.e. the enable_apicv check
> here should be unnecessary.
Right, it's more concise.  Thanks.

>> +}
>> +
>>   void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
>>   {
>>   	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
>>   
>> -	if (!vmx_can_use_vtd_pi(vcpu->kvm))
>> +	if (!(vmx_can_use_ipiv_pi(vcpu->kvm) || vmx_can_use_vtd_pi(vcpu->kvm)))
> Purely because I am beyond terrible at reading !(A || B) and !(A && B), can we
> write this as:
>
> 	if (!vmx_can_use_ipiv_pi(vcpu->kvm) && !vmx_can_use_vtd_pi(vcpu->kvm))
> 		return;
>
> Or better, add a helper.  We could even drop vmx_can_use_ipiv_pi() altogether, e.g.
>
> static bool vmx_can_use_posted_interrupts(struct kvm *kvm)
> {
> 	return irqchip_in_kernel(kvm) &&
> 	       (enable_ipiv || vmx_can_use_vtd_pi(kvm));
> }
>
> Or with both helpers:
>
> static bool vmx_can_use_posted_interrupts(struct kvm *kvm)
> {
> 	return vmx_can_use_ipiv_pi(kvm) || vmx_can_use_vtd_pi(kvm);
> }
>
> I don't think I have a strong preference over whether or not to drop
> vmx_can_use_ipiv_pi().  I think it's marginally easier to read with the extra
> helper?

I'd like to add helper without dropping vmx_can_use_ipiv_pi() which 
makes logic clear and independent.

>>   		return;
>>   
>>   	/* Set SN when the vCPU is preempted */
>> @@ -147,7 +152,7 @@ int pi_pre_block(struct kvm_vcpu *vcpu)
>>   	struct pi_desc old, new;
>>   	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
>>   
>> -	if (!vmx_can_use_vtd_pi(vcpu->kvm))
>> +	if (!(vmx_can_use_ipiv_pi(vcpu->kvm) || vmx_can_use_vtd_pi(vcpu->kvm)))
>>   		return 0;
>>   
>>   	WARN_ON(irqs_disabled());
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index 5716db9704c0..2e65464d6dee 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -104,6 +104,9 @@ module_param(fasteoi, bool, S_IRUGO);
>>   
>>   module_param(enable_apicv, bool, S_IRUGO);
>>   
>> +bool __read_mostly enable_ipiv = true;
>> +module_param(enable_ipiv, bool, 0444);
>> +
>>   /*
>>    * If nested=1, nested virtualization is supported, i.e., guests may use
>>    * VMX and be a hypervisor for its own guests. If nested=0, guests may not
>> @@ -224,6 +227,11 @@ static const struct {
>>   };
>>   
>>   #define L1D_CACHE_ORDER 4
>> +
>> +/* PID(Posted-Interrupt Descriptor)-pointer table entry is 64-bit long */
>> +#define MAX_PID_TABLE_ORDER get_order(KVM_MAX_VCPU_IDS * sizeof(u64))
>> +#define PID_TABLE_ENTRY_VALID 1
>> +
>>   static void *vmx_l1d_flush_pages;
>>   
>>   static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
>> @@ -2504,7 +2512,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>>   	}
>>   
>>   	if (_cpu_based_exec_control & CPU_BASED_ACTIVATE_TERTIARY_CONTROLS) {
>> -		u64 opt3 = 0;
>> +		u64 opt3 = TERTIARY_EXEC_IPI_VIRT;
>>   		u64 min3 = 0;
>>   
>>   		if (adjust_vmx_controls_64(min3, opt3,
>> @@ -3841,6 +3849,8 @@ static void vmx_update_msr_bitmap_x2apic(struct kvm_vcpu *vcpu)
>>   		vmx_enable_intercept_for_msr(vcpu, X2APIC_MSR(APIC_TMCCT), MSR_TYPE_RW);
>>   		vmx_disable_intercept_for_msr(vcpu, X2APIC_MSR(APIC_EOI), MSR_TYPE_W);
>>   		vmx_disable_intercept_for_msr(vcpu, X2APIC_MSR(APIC_SELF_IPI), MSR_TYPE_W);
>> +		vmx_set_intercept_for_msr(vcpu, X2APIC_MSR(APIC_ICR),
>> +				MSR_TYPE_RW, !enable_ipiv);
> Please align this, e.g.
>
> 		vmx_set_intercept_for_msr(vcpu, X2APIC_MSR(APIC_ICR),
> 					  MSR_TYPE_RW, !enable_ipiv);
>
> though I think I'd actually prefer we do:
>
>
> 		if (enable_ipiv)
> 			vmx_disable_intercept_for_msr(vcpu, X2APIC_MSR(APIC_ICR), MSR_TYPE_RW);
>
> and just let it poke out.  That makes it much more obvious that interception is
> disabled when IPI virtualization is enabled.  Using vmx_set_intercept_for_msr()
> implies that it could go either way, but that's not true as vmx_reset_x2apic_msrs()
> sets the bitmap to intercept all x2APIC MSRs.

Make sense. Will do.