Re: [PATCH v3 26/70] i386/tdx: Initialize TDX before creating TD vcpus

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Nov 15, 2023 at 02:14:35AM -0500, Xiaoyao Li wrote:
> Invoke KVM_TDX_INIT in kvm_arch_pre_create_vcpu() that KVM_TDX_INIT
> configures global TD configurations, e.g. the canonical CPUID config,
> and must be executed prior to creating vCPUs.
> 
> Use kvm_x86_arch_cpuid() to setup the CPUID settings for TDX VM.
> 
> Note, this doesn't address the fact that QEMU may change the CPUID
> configuration when creating vCPUs, i.e. punts on refactoring QEMU to
> provide a stable CPUID config prior to kvm_arch_init().
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
> Changes in v3:
> - Pass @errp in tdx_pre_create_vcpu() and pass error info to it. (Daniel)
> ---
>  accel/kvm/kvm-all.c        |  9 +++++++-
>  target/i386/kvm/kvm.c      |  9 ++++++++
>  target/i386/kvm/tdx-stub.c |  5 +++++
>  target/i386/kvm/tdx.c      | 45 ++++++++++++++++++++++++++++++++++++++
>  target/i386/kvm/tdx.h      |  4 ++++
>  5 files changed, 71 insertions(+), 1 deletion(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 6b5f4d62f961..a92fff471b58 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -441,8 +441,15 @@ int kvm_init_vcpu(CPUState *cpu, Error **errp)
>  
>      trace_kvm_init_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(cpu));
>  
> +    /*
> +     * tdx_pre_create_vcpu() may call cpu_x86_cpuid(). It in turn may call
> +     * kvm_vm_ioctl(). Set cpu->kvm_state in advance to avoid NULL pointer
> +     * dereference.
> +     */
> +    cpu->kvm_state = s;
>      ret = kvm_arch_pre_create_vcpu(cpu, errp);
>      if (ret < 0) {
> +        cpu->kvm_state = NULL;
>          goto err;
>      }
>  
> @@ -450,11 +457,11 @@ int kvm_init_vcpu(CPUState *cpu, Error **errp)
>      if (ret < 0) {
>          error_setg_errno(errp, -ret, "kvm_init_vcpu: kvm_get_vcpu failed (%lu)",
>                           kvm_arch_vcpu_id(cpu));
> +        cpu->kvm_state = NULL;
>          goto err;
>      }
>  
>      cpu->kvm_fd = ret;
> -    cpu->kvm_state = s;
>      cpu->vcpu_dirty = true;
>      cpu->dirty_pages = 0;
>      cpu->throttle_us_per_full = 0;
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index dafe4d262977..fc840653ceb6 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -2268,6 +2268,15 @@ int kvm_arch_init_vcpu(CPUState *cs)
>      return r;
>  }
>  
> +int kvm_arch_pre_create_vcpu(CPUState *cpu, Error **errp)
> +{
> +    if (is_tdx_vm()) {
> +        return tdx_pre_create_vcpu(cpu, errp);
> +    }
> +
> +    return 0;
> +}
> +
>  int kvm_arch_destroy_vcpu(CPUState *cs)
>  {
>      X86CPU *cpu = X86_CPU(cs);
> diff --git a/target/i386/kvm/tdx-stub.c b/target/i386/kvm/tdx-stub.c
> index 1d866d5496bf..3877d432a397 100644
> --- a/target/i386/kvm/tdx-stub.c
> +++ b/target/i386/kvm/tdx-stub.c
> @@ -6,3 +6,8 @@ int tdx_kvm_init(MachineState *ms, Error **errp)
>  {
>      return -EINVAL;
>  }
> +
> +int tdx_pre_create_vcpu(CPUState *cpu, Error **errp)
> +{
> +    return -EINVAL;
> +}
> diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
> index 1f5d8117d1a9..122a37c93de3 100644
> --- a/target/i386/kvm/tdx.c
> +++ b/target/i386/kvm/tdx.c
> @@ -467,6 +467,49 @@ int tdx_kvm_init(MachineState *ms, Error **errp)
>      return 0;
>  }
>  
> +int tdx_pre_create_vcpu(CPUState *cpu, Error **errp)
> +{
> +    MachineState *ms = MACHINE(qdev_get_machine());
> +    X86CPU *x86cpu = X86_CPU(cpu);
> +    CPUX86State *env = &x86cpu->env;
> +    struct kvm_tdx_init_vm *init_vm;

Mark this as auto-free to avoid the g_free() requirement

  g_autofree  struct kvm_tdx_init_vm *init_vm = NULL;

> +    int r = 0;
> +
> +    qemu_mutex_lock(&tdx_guest->lock);

   QEMU_LOCK_GUARD(&tdx_guest->lock);

to eliminate the mutex_unlock requirement, thus eliminating all
'goto' jumps and label targets, in favour of a plain 'return -1'
everywhere.

> +    if (tdx_guest->initialized) {
> +        goto out;
> +    }
> +
> +    init_vm = g_malloc0(sizeof(struct kvm_tdx_init_vm) +
> +                        sizeof(struct kvm_cpuid_entry2) * KVM_MAX_CPUID_ENTRIES);
> +
> +    r = kvm_vm_enable_cap(kvm_state, KVM_CAP_MAX_VCPUS, 0, ms->smp.cpus);
> +    if (r < 0) {
> +        error_setg(errp, "Unable to set MAX VCPUS to %d", ms->smp.cpus);
> +        goto out_free;
> +    }
> +
> +    init_vm->cpuid.nent = kvm_x86_arch_cpuid(env, init_vm->cpuid.entries, 0);
> +
> +    init_vm->attributes = tdx_guest->attributes;
> +
> +    do {
> +        r = tdx_vm_ioctl(KVM_TDX_INIT_VM, 0, init_vm);
> +    } while (r == -EAGAIN);
> +    if (r < 0) {
> +        error_setg_errno(errp, -r, "KVM_TDX_INIT_VM failed");
> +        goto out_free;
> +    }
> +
> +    tdx_guest->initialized = true;
> +
> +out_free:
> +    g_free(init_vm);
> +out:
> +    qemu_mutex_unlock(&tdx_guest->lock);
> +    return r;
> +}
> +
>  /* tdx guest */
>  OBJECT_DEFINE_TYPE_WITH_INTERFACES(TdxGuest,
>                                     tdx_guest,
> @@ -479,6 +522,8 @@ static void tdx_guest_init(Object *obj)
>  {
>      TdxGuest *tdx = TDX_GUEST(obj);
>  
> +    qemu_mutex_init(&tdx->lock);
> +
>      tdx->attributes = 0;
>  }
>  
> diff --git a/target/i386/kvm/tdx.h b/target/i386/kvm/tdx.h
> index 06599b65b827..432077723ac5 100644
> --- a/target/i386/kvm/tdx.h
> +++ b/target/i386/kvm/tdx.h
> @@ -17,6 +17,9 @@ typedef struct TdxGuestClass {
>  typedef struct TdxGuest {
>      ConfidentialGuestSupport parent_obj;
>  
> +    QemuMutex lock;
> +
> +    bool initialized;
>      uint64_t attributes;    /* TD attributes */
>  } TdxGuest;
>  
> @@ -29,5 +32,6 @@ bool is_tdx_vm(void);
>  int tdx_kvm_init(MachineState *ms, Error **errp);
>  void tdx_get_supported_cpuid(uint32_t function, uint32_t index, int reg,

>                               uint32_t *ret);
> +int tdx_pre_create_vcpu(CPUState *cpu, Error **errp);
>  
>  #endif /* QEMU_I386_TDX_H */
> -- 
> 2.34.1
> 

With regards,
Daniel
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