Date:   Mon, 27 Feb 2023 15:49:14 -0800
From:   Isaku Yamahata <isaku.yamahata@gmail.com>
To:     Zhi Wang <zhi.wang.linux@gmail.com>
Cc:     isaku.yamahata@intel.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, isaku.yamahata@gmail.com,
        Paolo Bonzini <pbonzini@redhat.com>, erdemaktas@google.com,
        Sean Christopherson <seanjc@google.com>,
        Sagi Shahar <sagis@google.com>,
        David Matlack <dmatlack@google.com>
Subject: Re: [PATCH v11 023/113] KVM: TDX: allocate/free TDX vcpu structure
Message-ID: <20230227234914.GU4175971@ls.amr.corp.intel.com>
References: <cover.1673539699.git.isaku.yamahata@intel.com>
 <db53b2c6c7718df7df89bb36b83257a2588b58e1.1673539699.git.isaku.yamahata@intel.com>
 <20230116124606.00003872@gmail.com>
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On Mon, Jan 16, 2023 at 12:46:06PM +0200,
Zhi Wang <zhi.wang.linux@gmail.com> wrote:

> 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);
> ----
> 
> ?

It's C11.  I updated the code to not use the feature.


> >  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?

I converted vm_bugged to KVM_BUG_ON.  Because the td_bugged case shouldn't
happen for TDX case, it's worthwhile for KVM_BUG_ON()


> 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);
>         }

No. Because I'm trying to contain is_td/is_td_vcpu in vmx specific and not use
in common x86 code.


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

because LAPIC_MODE_X2APIC includes MSR_IA32_APICBASE_ENABLE.
In lapic.h
        LAPIC_MODE_X2APIC = MSR_IA32_APICBASE_ENABLE | X2APIC_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.

I converted it into KVM_BUG_ON().


> 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)
> >  {
> 

-- 
Isaku Yamahata <isaku.yamahata@gmail.com>