Re: [PATCH v18 023/121] KVM: TDX: Make KVM_CAP_MAX_VCPUS backend specific

From: Yuan Yao
Date: Thu Feb 01 2024 - 01:16:38 EST

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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@xxxxxxxxx wrote:
> > From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> >
> > 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@xxxxxxxxx>
> > ---
> > 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;
>
>

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