Re: [PATCH v8 08/55] i386/tdx: Initialize TDX before creating TD vcpus

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

On Tue, Apr 01, 2025 at 09:01:18AM -0400, Xiaoyao Li wrote:
> Invoke KVM_TDX_INIT_VM in kvm_arch_pre_create_vcpu() that
> KVM_TDX_INIT_VM 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>
> Acked-by: Markus Armbruster <armbru@redhat.com>
> ---
> Changes in v8:
> - Drop the code that initializes cpu->kvm_state before
>   kvm_arch_pre_create_vcpu() because it's not needed anymore.
> 
> Changes in v7:
> - Add comments to explain why KVM_TDX_INIT_VM should retry on -EAGAIN;
> - Add retry limit of 10000 times for -EAGAIN on KVM_TDX_INIT_VM;
> 
> Changes in v6:
> - setup xfam explicitly to fit with new uapi;
> - use tdx_caps->cpuid to filter the input of cpuids because now KVM only
>   allows the leafs that reported via KVM_TDX_GET_CAPABILITIES;
> 
> Changes in v4:
> - mark init_vm with g_autofree() and use QEMU_LOCK_GUARD() to eliminate
>   the goto labels; (Daniel)
> Changes in v3:
> - Pass @errp in tdx_pre_create_vcpu() and pass error info to it. (Daniel)
> ---
>  target/i386/kvm/kvm.c       |  16 +++---
>  target/i386/kvm/kvm_i386.h  |   5 ++
>  target/i386/kvm/meson.build |   2 +-
>  target/i386/kvm/tdx-stub.c  |  10 ++++
>  target/i386/kvm/tdx.c       | 105 ++++++++++++++++++++++++++++++++++++
>  target/i386/kvm/tdx.h       |   6 +++
>  6 files changed, 137 insertions(+), 7 deletions(-)
>  create mode 100644 target/i386/kvm/tdx-stub.c


> diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
> index 16f67e18ae78..0afaf739c09f 100644
> --- a/target/i386/kvm/tdx.c
> +++ b/target/i386/kvm/tdx.c

> +int tdx_pre_create_vcpu(CPUState *cpu, Error **errp)
> +{
> +    X86CPU *x86cpu = X86_CPU(cpu);
> +    CPUX86State *env = &x86cpu->env;
> +    g_autofree struct kvm_tdx_init_vm *init_vm = NULL;
> +    Error *local_err = NULL;
> +    int retry = 10000;
> +    int r = 0;
> +
> +    QEMU_LOCK_GUARD(&tdx_guest->lock);
> +    if (tdx_guest->initialized) {
> +        return r;
> +    }
> +
> +    init_vm = g_malloc0(sizeof(struct kvm_tdx_init_vm) +
> +                        sizeof(struct kvm_cpuid_entry2) * KVM_MAX_CPUID_ENTRIES);
> +
> +    r = setup_td_xfam(x86cpu, errp);
> +    if (r) {
> +        return r;
> +    }
> +
> +    init_vm->cpuid.nent = kvm_x86_build_cpuid(env, init_vm->cpuid.entries, 0);
> +    tdx_filter_cpuid(&init_vm->cpuid);
> +
> +    init_vm->attributes = tdx_guest->attributes;
> +    init_vm->xfam = tdx_guest->xfam;
> +
> +    /*
> +     * KVM_TDX_INIT_VM gets -EAGAIN when KVM side SEAMCALL(TDH_MNG_CREATE)
> +     * gets TDX_RND_NO_ENTROPY due to Random number generation (e.g., RDRAND or
> +     * RDSEED) is busy.
> +     *
> +     * Retry for the case.
> +     */
> +    do {
> +        error_free(local_err);
> +        local_err = NULL;
> +        r = tdx_vm_ioctl(KVM_TDX_INIT_VM, 0, init_vm, &local_err);
> +    } while (r == -EAGAIN && --retry);
> +
> +    if (r < 0) {
> +        if (!retry) {
> +            error_report("Hardware RNG (Random Number Generator) is busy "
> +                         "occupied by someone (via RDRAND/RDSEED) maliciously, "
> +                         "which leads to KVM_TDX_INIT_VM keeping failure "
> +                         "due to lack of entropy.");

This needs to be

     error_append_hint(local_err, ....);

so that this message gets associated with the error object that
is propagated, and the top level will print it all at once.

> +        }
> +        error_propagate(errp, local_err);
> +        return r;
> +    }
> +
> +    tdx_guest->initialized = true;
> +
> +    return 0;
> +}

With regards,
Daniel
-- 
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