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Message-ID: <41ff6a9a-c32b-41f1-9d72-e26f2008acf3@linux.intel.com>
Date: Mon, 11 Dec 2023 17:22:40 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: isaku.yamahata@...el.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
Sagi Shahar <sagis@...gle.com>,
David Matlack <dmatlack@...gle.com>,
Kai Huang <kai.huang@...el.com>,
Zhi Wang <zhi.wang.linux@...il.com>, chen.bo@...el.com,
hang.yuan@...el.com, tina.zhang@...el.com
Subject: Re: [PATCH v17 019/116] KVM: x86, tdx: Make KVM_CAP_MAX_VCPUS backend
specific
On 11/7/2023 10:55 PM, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata<isaku.yamahata@...el.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.
Should use "TDX" instread of "x86, tdx" in shortlog?
> Signed-off-by: Isaku Yamahata<isaku.yamahata@...el.com>
> ---
> 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 | 5 +++++
> arch/x86/kvm/x86.c | 4 ++++
> 7 files changed, 68 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> index 09abb53d92ea..b7b591f1ff72 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 6509e967454a..f240c3d025b1 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1574,7 +1574,9 @@ 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 a95bbd10c3d8..5a857c8defd9 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 min3(kvm->max_vcpus, KVM_MAX_VCPUS, TDX_MAX_VCPUS);
kvm->max_vcpus is initialized to KVM_MAX_VCPUS when kvm_create_vm().
Also, when userspace tries to set the value, it's also limited by KVM_MAX_VCPUS.
So, for x86, the value is <= KVM_MAX_VCPUS for sure.
It could be simpler:
+ if (is_td(kvm))
+ return min(kvm->max_vcpus, TDX_MAX_VCPUS);
> +
> + return kvm->max_vcpus;
> +}
> +
> static int vt_hardware_enable(void)
> {
> int ret;
> @@ -43,6 +55,14 @@ 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))
> @@ -80,7 +100,9 @@ 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 f9e80582865d..331fbaa10d46 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -17,6 +17,36 @@
> 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;
Can merge the two if statements into one.
+ 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/tdx.h b/arch/x86/kvm/vmx/tdx.h
> index 473013265bd8..22c0b57f69ca 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 6487884a8d8e..ee5d8a38e7f8 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -138,11 +138,16 @@ void vmx_setup_mce(struct kvm_vcpu *vcpu);
> int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops);
> 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 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 ced75e9204b9..de6e6462e7f3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4694,6 +4694,8 @@ 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;
> @@ -6641,6 +6643,8 @@ 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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