Re: [PATCH v11 023/113] KVM: TDX: allocate/free TDX vcpu structure

[Zhi Wang <zhi.wang.linux@gmail.com>]

On Thu, 12 Jan 2023 08:31:31 -0800
isaku.yamahata@intel.com wrote:

> From: Isaku Yamahata <isaku.yamahata@intel.com>
> 
> The next step of TDX guest creation is to create vcpu.  Allocate TDX vcpu
> structures, partially initialize it.  Allocate pages of TDX vcpu for the
> TDX module.  Actual donation TDX vcpu pages to the TDX module is not done
> yet.
> 
> In the case of the conventional case, cpuid is empty at the initialization.
> and cpuid is configured after the vcpu initialization.  Because TDX
> supports only X2APIC mode, cpuid is forcibly initialized to support X2APIC
> on the vcpu initialization.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
> Changes v10 -> v11:
> - NULL check of kvmalloc_array() in tdx_vcpu_reset. Move it to
>   tdx_vcpu_create()
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
>  arch/x86/kvm/vmx/main.c    | 40 ++++++++++++++++++--
>  arch/x86/kvm/vmx/tdx.c     | 75 ++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/vmx/x86_ops.h | 10 +++++
>  arch/x86/kvm/x86.c         |  2 +
>  4 files changed, 123 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index ddf0742f1f67..59813ca05f36 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -63,6 +63,38 @@ static void vt_vm_free(struct kvm *kvm)
>  		tdx_vm_free(kvm);
>  }
>  
> +static int vt_vcpu_precreate(struct kvm *kvm)
> +{
> +	if (is_td(kvm))
> +		return 0;
> +
> +	return vmx_vcpu_precreate(kvm);
> +}
> +
> +static int vt_vcpu_create(struct kvm_vcpu *vcpu)
> +{
> +	if (is_td_vcpu(vcpu))
> +		return tdx_vcpu_create(vcpu);
> +
> +	return vmx_vcpu_create(vcpu);
> +}
> +

-----
> +static void vt_vcpu_free(struct kvm_vcpu *vcpu)
> +{
> +	if (is_td_vcpu(vcpu))
> +		return tdx_vcpu_free(vcpu);
> +
> +	return vmx_vcpu_free(vcpu);
> +}
> +
> +static void vt_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> +{
> +	if (is_td_vcpu(vcpu))
> +		return tdx_vcpu_reset(vcpu, init_event);
> +
> +	return vmx_vcpu_reset(vcpu, init_event);
> +}
> +
----

It seems a little strange to use return in this style. Would it be better like:

-----
if (xxx) {
	tdx_vcpu_reset(xxx);
	return; 
}

vmx_vcpu_reset(xxx);
----

?

>  static int vt_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
>  {
>  	if (!is_td(kvm))
> @@ -90,10 +122,10 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>  	.vm_destroy = vt_vm_destroy,
>  	.vm_free = vt_vm_free,
>  
> -	.vcpu_precreate = vmx_vcpu_precreate,
> -	.vcpu_create = vmx_vcpu_create,
> -	.vcpu_free = vmx_vcpu_free,
> -	.vcpu_reset = vmx_vcpu_reset,
> +	.vcpu_precreate = vt_vcpu_precreate,
> +	.vcpu_create = vt_vcpu_create,
> +	.vcpu_free = vt_vcpu_free,
> +	.vcpu_reset = vt_vcpu_reset,
>  
>  	.prepare_switch_to_guest = vmx_prepare_switch_to_guest,
>  	.vcpu_load = vmx_vcpu_load,
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 557a609c5147..099f0737a5aa 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -281,6 +281,81 @@ int tdx_vm_init(struct kvm *kvm)
>  	return 0;
>  }
>  
> +int tdx_vcpu_create(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_cpuid_entry2 *e;
> +
> +	/*
> +	 * On cpu creation, cpuid entry is blank.  Forcibly enable
> +	 * X2APIC feature to allow X2APIC.
> +	 * Because vcpu_reset() can't return error, allocation is done here.
> +	 */
> +	WARN_ON_ONCE(vcpu->arch.cpuid_entries);
> +	WARN_ON_ONCE(vcpu->arch.cpuid_nent);
> +	e = kvmalloc_array(1, sizeof(*e), GFP_KERNEL_ACCOUNT);
> +	if (!e)
> +		return -ENOMEM;
> +	*e  = (struct kvm_cpuid_entry2) {
> +		.function = 1,	/* Features for X2APIC */
> +		.index = 0,
> +		.eax = 0,
> +		.ebx = 0,
> +		.ecx = 1ULL << 21,	/* X2APIC */
> +		.edx = 0,
> +	};
> +	vcpu->arch.cpuid_entries = e;
> +	vcpu->arch.cpuid_nent = 1;
> +
> +	/* TDX only supports x2APIC, which requires an in-kernel local APIC. */
> +	if (!vcpu->arch.apic)
> +		return -EINVAL;
> +
> +	fpstate_set_confidential(&vcpu->arch.guest_fpu);
> +
> +	vcpu->arch.efer = EFER_SCE | EFER_LME | EFER_LMA | EFER_NX;
> +
> +	vcpu->arch.cr0_guest_owned_bits = -1ul;
> +	vcpu->arch.cr4_guest_owned_bits = -1ul;
> +
> +	vcpu->arch.tsc_offset = to_kvm_tdx(vcpu->kvm)->tsc_offset;
> +	vcpu->arch.l1_tsc_offset = vcpu->arch.tsc_offset;
> +	vcpu->arch.guest_state_protected =
> +		!(to_kvm_tdx(vcpu->kvm)->attributes & TDX_TD_ATTRIBUTE_DEBUG);
> +
> +	return 0;
> +}
> +
> +void tdx_vcpu_free(struct kvm_vcpu *vcpu)
> +{
> +	/* This is stub for now.  More logic will come. */
> +}
> +
> +void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> +{
> +	struct msr_data apic_base_msr;
> +
> +	/* TDX doesn't support INIT event. */
> +	if (WARN_ON_ONCE(init_event))
> +		goto td_bugged;
> +
> +	/* TDX rquires X2APIC. */
                ^
               requires
> +	apic_base_msr.data = APIC_DEFAULT_PHYS_BASE | LAPIC_MODE_X2APIC;
> +	if (kvm_vcpu_is_reset_bsp(vcpu))
> +		apic_base_msr.data |= MSR_IA32_APICBASE_BSP;
> +	apic_base_msr.host_initiated = true;
> +	if (WARN_ON_ONCE(kvm_set_apic_base(vcpu, &apic_base_msr)))
> +		goto td_bugged;
> +
> +	/*
> +	 * Don't update mp_state to runnable because more initialization
> +	 * is needed by TDX_VCPU_INIT.
> +	 */
> +	return;
> +
> +td_bugged:
> +	vcpu->kvm->vm_bugged = true;
> +}
> +

1) Using vm_bugged to terminate the VM creation feels off. When
using it in creation path, the termination still happens in xx_vcpu_run().

Thus, even something wrong happens at a certain point of the creation path,
the VM creation still continues. Until the xxx_vcpu_run(), the VM termination
finally happens.

Why not just fail in the creation path?

2) Move 

> +	apic_base_msr.data = APIC_DEFAULT_PHYS_BASE | LAPIC_MODE_X2APIC;
> +	if (kvm_vcpu_is_reset_bsp(vcpu))
> +		apic_base_msr.data |= MSR_IA32_APICBASE_BSP;
> +	apic_base_msr.host_initiated = true;

to:

void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
{
        struct kvm_lapic *apic = vcpu->arch.apic;
        u64 msr_val;
        int i;

        if (!init_event) {
                msr_val = APIC_DEFAULT_PHYS_BASE | MSR_IA32_APICBASE_ENABLE;

		/* here */
		if (is_td_vcpu(vcpu)) 
			msr_val = xxxx;
                if (kvm_vcpu_is_reset_bsp(vcpu))
                        msr_val |= MSR_IA32_APICBASE_BSP;
                kvm_lapic_set_base(vcpu, msr_val);
        }

PS: Is there any reason that APIC MSR in TDX doesn't need
MSR_IA32_APICBASE_ENABLE?

3) Change the following:

> +
> +	/* TDX doesn't support INIT event. */
> +	if (WARN_ON_ONCE(init_event))
> +		goto td_bugged;
> +

to 
	WARN_ON_ONCE(init_event);

kvm_cpu_deliver_init() will trigger a kvm_vcpu_reset(xxx, init_event=true),
but you have already avoided this in vt_vcpu_deliver_init(). A warn
is good enough to remind people.

With these changes, tdx_vcpu_reset() will only contain the CPUID configuration
, using the vm_bugged to terminate the VM in tdx_vcpu_reset() can be removed.

>  int tdx_dev_ioctl(void __user *argp)
>  {
>  	struct kvm_tdx_capabilities __user *user_caps;
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index 6c40dda1cc2f..37ab2cfd35bc 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -147,7 +147,12 @@ int tdx_offline_cpu(void);
>  int tdx_vm_init(struct kvm *kvm);
>  void tdx_mmu_release_hkid(struct kvm *kvm);
>  void tdx_vm_free(struct kvm *kvm);
> +
>  int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
> +
> +int tdx_vcpu_create(struct kvm_vcpu *vcpu);
> +void tdx_vcpu_free(struct kvm_vcpu *vcpu);
> +void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
>  #else
>  static inline int tdx_hardware_setup(struct kvm_x86_ops *x86_ops) { return 0; }
>  static inline void tdx_hardware_unsetup(void) {}
> @@ -159,7 +164,12 @@ static inline int tdx_vm_init(struct kvm *kvm) { return -EOPNOTSUPP; }
>  static inline void tdx_mmu_release_hkid(struct kvm *kvm) {}
>  static inline void tdx_flush_shadow_all_private(struct kvm *kvm) {}
>  static inline void tdx_vm_free(struct kvm *kvm) {}
> +
>  static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOPNOTSUPP; }
> +
> +static inline int tdx_vcpu_create(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; }
> +static inline void tdx_vcpu_free(struct kvm_vcpu *vcpu) {}
> +static inline void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) {}
>  #endif
>  
>  #endif /* __KVM_X86_VMX_X86_OPS_H */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1fb135e0c98f..e8bc66031a1d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -492,6 +492,7 @@ int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	kvm_recalculate_apic_map(vcpu->kvm);
>  	return 0;
>  }
> +EXPORT_SYMBOL_GPL(kvm_set_apic_base);
>  
>  /*
>   * Handle a fault on a hardware virtualization (VMX or SVM) instruction.
> @@ -12109,6 +12110,7 @@ bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu)
>  {
>  	return vcpu->kvm->arch.bsp_vcpu_id == vcpu->vcpu_id;
>  }
> +EXPORT_SYMBOL_GPL(kvm_vcpu_is_reset_bsp);
>

The symbols don't need to be exported with the changes mentioned above.
  
>  bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu)
>  {