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Date: Thu, 1 Feb 2024 14:16:22 +0800
From: Yuan Yao <yuan.yao@linux.intel.com>
To: Binbin Wu <binbin.wu@linux.intel.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>, Kai Huang <kai.huang@intel.com>,
	chen.bo@intel.com, hang.yuan@intel.com, tina.zhang@intel.com
Subject: Re: [PATCH v18 023/121] KVM: TDX: Make KVM_CAP_MAX_VCPUS backend
 specific
Message-ID: <20240201061622.hvun7amakvbplmsb@yy-desk-7060>
References: <cover.1705965634.git.isaku.yamahata@intel.com>
 <ed33ebe29b231e8e657cd610a983fa603b10f530.1705965634.git.isaku.yamahata@intel.com>
 <7cc28677-f7d1-4aba-8557-66c685115074@linux.intel.com>
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On Wed, Jan 24, 2024 at 09:17:15AM +0800, Binbin Wu wrote:
>
>
> On 1/23/2024 7:52 AM, isaku.yamahata@intel.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@intel.com>
> >
> > TDX has its own limitation on the maximum number of vcpus that the guest
> > can accommodate.  Allow x86 kvm backend to implement its own KVM_ENABLE_CAP
> > handler and implement TDX backend for KVM_CAP_MAX_VCPUS.  user space VMM,
> > e.g. qemu, can specify its value instead of KVM_MAX_VCPUS.
> For legacy VM, KVM just provides the interface to query the max_vcpus.
> Why TD needs to provide a interface for userspace to set the limitation?
> What's the scenario?

I think the reason is TDH.MNG.INIT needs it:

TD_PARAMS:
    MAX_VCPUS:
        offset: 16 bytes.
        type: Unsigned 16b Integer.
        size: 2.
        Description: Maximum number of VCPUs.

May better to clarify this in the commit yet.

>
>
> >
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > ---
> > v18:
> > - use TDX instead of "x86, tdx" in subject
> > - use min(max_vcpu, TDX_MAX_VCPU) instead of
> >    min3(max_vcpu, KVM_MAX_VCPU, TDX_MAX_VCPU)
> > - make "if (KVM_MAX_VCPU) and if (TDX_MAX_VCPU)" into one if statement
> > ---
> >   arch/x86/include/asm/kvm-x86-ops.h |  2 ++
> >   arch/x86/include/asm/kvm_host.h    |  2 ++
> >   arch/x86/kvm/vmx/main.c            | 22 ++++++++++++++++++++++
> >   arch/x86/kvm/vmx/tdx.c             | 29 +++++++++++++++++++++++++++++
> >   arch/x86/kvm/vmx/x86_ops.h         |  5 +++++
> >   arch/x86/kvm/x86.c                 |  4 ++++
> >   6 files changed, 64 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> > index 943b21b8b106..2f976c0f3116 100644
> > --- a/arch/x86/include/asm/kvm-x86-ops.h
> > +++ b/arch/x86/include/asm/kvm-x86-ops.h
> > @@ -21,6 +21,8 @@ KVM_X86_OP(hardware_unsetup)
> >   KVM_X86_OP(has_emulated_msr)
> >   KVM_X86_OP(vcpu_after_set_cpuid)
> >   KVM_X86_OP(is_vm_type_supported)
> > +KVM_X86_OP_OPTIONAL(max_vcpus);
> > +KVM_X86_OP_OPTIONAL(vm_enable_cap)
> >   KVM_X86_OP(vm_init)
> >   KVM_X86_OP_OPTIONAL(vm_destroy)
> >   KVM_X86_OP_OPTIONAL_RET0(vcpu_precreate)
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 26f4668b0273..db44a92e5659 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1602,7 +1602,9 @@ struct kvm_x86_ops {
> >   	void (*vcpu_after_set_cpuid)(struct kvm_vcpu *vcpu);
> >   	bool (*is_vm_type_supported)(unsigned long vm_type);
> > +	int (*max_vcpus)(struct kvm *kvm);
> >   	unsigned int vm_size;
> > +	int (*vm_enable_cap)(struct kvm *kvm, struct kvm_enable_cap *cap);
> >   	int (*vm_init)(struct kvm *kvm);
> >   	void (*vm_destroy)(struct kvm *kvm);
> > diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> > index 50da807d7aea..4611f305a450 100644
> > --- a/arch/x86/kvm/vmx/main.c
> > +++ b/arch/x86/kvm/vmx/main.c
> > @@ -6,6 +6,7 @@
> >   #include "nested.h"
> >   #include "pmu.h"
> >   #include "tdx.h"
> > +#include "tdx_arch.h"
> >   static bool enable_tdx __ro_after_init;
> >   module_param_named(tdx, enable_tdx, bool, 0444);
> > @@ -16,6 +17,17 @@ static bool vt_is_vm_type_supported(unsigned long type)
> >   		(enable_tdx && tdx_is_vm_type_supported(type));
> >   }
> > +static int vt_max_vcpus(struct kvm *kvm)
> > +{
> > +	if (!kvm)
> > +		return KVM_MAX_VCPUS;
> > +
> > +	if (is_td(kvm))
> > +		return min(kvm->max_vcpus, TDX_MAX_VCPUS);
> > +
> > +	return kvm->max_vcpus;
> > +}
> > +
> >   static int vt_hardware_enable(void)
> >   {
> >   	int ret;
> > @@ -54,6 +66,14 @@ static void vt_hardware_unsetup(void)
> >   	vmx_hardware_unsetup();
> >   }
> > +static int vt_vm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
> > +{
> > +	if (is_td(kvm))
> > +		return tdx_vm_enable_cap(kvm, cap);
> > +
> > +	return -EINVAL;
> > +}
> > +
> >   static int vt_vm_init(struct kvm *kvm)
> >   {
> >   	if (is_td(kvm))
> > @@ -91,7 +111,9 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
> >   	.has_emulated_msr = vmx_has_emulated_msr,
> >   	.is_vm_type_supported = vt_is_vm_type_supported,
> > +	.max_vcpus = vt_max_vcpus,
> >   	.vm_size = sizeof(struct kvm_vmx),
> > +	.vm_enable_cap = vt_vm_enable_cap,
> >   	.vm_init = vt_vm_init,
> >   	.vm_destroy = vmx_vm_destroy,
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 8c463407f8a8..876ad7895b88 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -100,6 +100,35 @@ struct tdx_info {
> >   /* Info about the TDX module. */
> >   static struct tdx_info *tdx_info;
> > +int tdx_vm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
> > +{
> > +	int r;
> > +
> > +	switch (cap->cap) {
> > +	case KVM_CAP_MAX_VCPUS: {
> > +		if (cap->flags || cap->args[0] == 0)
> > +			return -EINVAL;
> > +		if (cap->args[0] > KVM_MAX_VCPUS ||
> > +		    cap->args[0] > TDX_MAX_VCPUS)
> > +			return -E2BIG;
> > +
> > +		mutex_lock(&kvm->lock);
> > +		if (kvm->created_vcpus)
> > +			r = -EBUSY;
> > +		else {
> > +			kvm->max_vcpus = cap->args[0];
> > +			r = 0;
> > +		}
> > +		mutex_unlock(&kvm->lock);
> > +		break;
> > +	}
> > +	default:
> > +		r = -EINVAL;
> > +		break;
> > +	}
> > +	return r;
> > +}
> > +
> >   static int tdx_get_capabilities(struct kvm_tdx_cmd *cmd)
> >   {
> >   	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 6e238142b1e8..3a3be66888da 100644
> > --- a/arch/x86/kvm/vmx/x86_ops.h
> > +++ b/arch/x86/kvm/vmx/x86_ops.h
> > @@ -139,12 +139,17 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops);
> >   void tdx_hardware_unsetup(void);
> >   bool tdx_is_vm_type_supported(unsigned long type);
> > +int tdx_vm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap);
> >   int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
> >   #else
> >   static inline int tdx_hardware_setup(struct kvm_x86_ops *x86_ops) { return -EOPNOTSUPP; }
> >   static inline void tdx_hardware_unsetup(void) {}
> >   static inline bool tdx_is_vm_type_supported(unsigned long type) { return false; }
> > +static inline int tdx_vm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
> > +{
> > +	return -EINVAL;
> > +};
> >   static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOPNOTSUPP; }
> >   #endif
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index dd3a23d56621..a1389ddb1b33 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -4726,6 +4726,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >   		break;
> >   	case KVM_CAP_MAX_VCPUS:
> >   		r = KVM_MAX_VCPUS;
> > +		if (kvm_x86_ops.max_vcpus)
> > +			r = static_call(kvm_x86_max_vcpus)(kvm);
> >   		break;
> >   	case KVM_CAP_MAX_VCPU_ID:
> >   		r = KVM_MAX_VCPU_IDS;
> > @@ -6683,6 +6685,8 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> >   		break;
> >   	default:
> >   		r = -EINVAL;
> > +		if (kvm_x86_ops.vm_enable_cap)
> > +			r = static_call(kvm_x86_vm_enable_cap)(kvm, cap);
> >   		break;
> >   	}
> >   	return r;
>
>