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

Daniel P. Berrangé
2023-11-15T11:01:46Z

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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