Re: [PATCH v13 018/113] KVM: x86, tdx: Make KVM_CAP_MAX_VCPUS backend specific

From: Zhi Wang
Date: Sat Mar 25 2023 - 14:13:35 EST

On Sun, 12 Mar 2023 10:55:42 -0700
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.
>

I think enabling the cap here is actually "configuring the cap". KVM_CAP_MAX
_VCPUS is actually always enabled whether userspace enables it or not. It
would be nice to configure of the max VCPUS in kvm_arch_vm_ioctl() where
routines of configuring a VM should belong. E.g. KVM_SET_MAX_VCPUS.

> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
> 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 | 30 ++++++++++++++++++++++++++++++
> arch/x86/kvm/vmx/tdx.h | 3 +++
> arch/x86/kvm/vmx/x86_ops.h | 2 ++
> arch/x86/kvm/x86.c | 4 ++++
> 7 files changed, 65 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> index 58fbaa05fc8c..7522c193f2b4 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 49e3ca89aced..d98d61e5213d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1562,7 +1562,9 @@ 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 8ddd263eeabc..68bb320d0b6d 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);
> @@ -29,6 +30,17 @@ 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 min3(kvm->max_vcpus, KVM_MAX_VCPUS, TDX_MAX_VCPUS);
> +
> + return kvm->max_vcpus;
> +}
> +
> static __init int vt_hardware_setup(void)
> {
> int ret;
> @@ -42,6 +54,14 @@ static __init int vt_hardware_setup(void)
> return 0;
> }
>
> +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))
> @@ -81,7 +101,9 @@ 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 d759028a698e..8b02e605cfb5 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -16,6 +16,36 @@
> offsetof(struct tdsysinfo_struct, cpuid_configs)) \
> / sizeof(struct tdx_cpuid_config))
>
> +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)
> + return -E2BIG;
> + if (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;
> +}
> +
> int tdx_hardware_enable(void)
> {
> return tdx_cpu_enable();
> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> index 2210c8c1e893..3860aa351bd9 100644
> --- a/arch/x86/kvm/vmx/tdx.h
> +++ b/arch/x86/kvm/vmx/tdx.h
> @@ -3,6 +3,9 @@
> #define __KVM_X86_TDX_H
>
> #ifdef CONFIG_INTEL_TDX_HOST
> +
> +#include "tdx_ops.h"
> +
> struct kvm_tdx {
> struct kvm kvm;
> /* TDX specific members follow. */
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index c70749114e9e..8118647aa8ca 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -143,6 +143,7 @@ int tdx_hardware_enable(void);
> bool tdx_is_vm_type_supported(unsigned long type);
> int tdx_dev_ioctl(void __user *argp);
>
> +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 -ENOSYS; }
> @@ -150,6 +151,7 @@ static inline int tdx_hardware_enable(void) { return -EOPNOTSUPP; }
> static inline bool tdx_is_vm_type_supported(unsigned long type) { return false; }
> static inline int tdx_dev_ioctl(void __user *argp) { return -EOPNOTSUPP; };
>
> +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 8687623929c3..7b02dd40ef21 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4500,6 +4500,8 @@ 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;
> @@ -6439,6 +6441,8 @@ 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;