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    SubjectRe: [PATCH v19 076/130] KVM: TDX: Finalize VM initialization
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    On 26/02/24 10:26, isaku.yamahata@intel.com wrote:
    > From: Isaku Yamahata <isaku.yamahata@intel.com>
    >
    > To protect the initial contents of the guest TD, the TDX module measures
    > the guest TD during the build process as SHA-384 measurement. The
    > measurement of the guest TD contents needs to be completed to make the
    > guest TD ready to run.
    >
    > Add a new subcommand, KVM_TDX_FINALIZE_VM, for VM-scoped
    > KVM_MEMORY_ENCRYPT_OP to finalize the measurement and mark the TDX VM ready
    > to run.

    Perhaps a spruced up commit message would be:

    <BEGIN>
    Add a new VM-scoped KVM_MEMORY_ENCRYPT_OP IOCTL subcommand,
    KVM_TDX_FINALIZE_VM, to perform TD Measurement Finalization.

    Documentation for the API is added in another patch:
    "Documentation/virt/kvm: Document on Trust Domain Extensions(TDX)"

    For the purpose of attestation, a measurement must be made of the TDX VM
    initial state. This is referred to as TD Measurement Finalization, and
    uses SEAMCALL TDH.MR.FINALIZE, after which:
    1. The VMM adding TD private pages with arbitrary content is no longer
    allowed
    2. The TDX VM is runnable
    <END>

    History:

    This code is essentially unchanged from V1, as below.
    Except for V5, the code has never had any comments.
    Paolo's comment from then still appears unaddressed.

    V19: Unchanged
    V18: Undoes change of V17
    V17: Also change tools/arch/x86/include/uapi/asm/kvm.h
    V16: Unchanged
    V15: Undoes change of V10
    V11-V14: Unchanged
    V10: Adds a hack (related to TDH_MEM_TRACK)
    that was later removed in V15
    V6-V9: Unchanged
    V5 Broke out the code into a separate patch and
    received its only comments, which were from Paolo:

    "Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
    Note however that errors should be passed back in the struct."

    This presumably refers to struct kvm_tdx_cmd which has an "error"
    member, but that is not updated by tdx_td_finalizemr()

    V4 was a cut-down series and the code was not present
    V3 introduced WARN_ON_ONCE for the error condition
    V2 accommodated renaming the seamcall function and ID

    Outstanding:

    1. Address Paolo's comment about the error code
    2. Is WARN_ON sensible?

    Final note:

    It might be possible to make TD Measurement Finalization
    transparent to the user space VMM and forego another API, but it seems
    doubtful that would really make anything much simpler.

    >
    > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
    >
    > ---
    > v18:
    > - Remove the change of tools/arch/x86/include/uapi/asm/kvm.h.
    >
    > v14 -> v15:
    > - removed unconditional tdx_track() by tdx_flush_tlb_current() that
    > does tdx_track().
    >
    > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
    > ---
    > arch/x86/include/uapi/asm/kvm.h | 1 +
    > arch/x86/kvm/vmx/tdx.c | 21 +++++++++++++++++++++
    > 2 files changed, 22 insertions(+)
    >
    > diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
    > index 34167404020c..c160f60189d1 100644
    > --- a/arch/x86/include/uapi/asm/kvm.h
    > +++ b/arch/x86/include/uapi/asm/kvm.h
    > @@ -573,6 +573,7 @@ enum kvm_tdx_cmd_id {
    > KVM_TDX_INIT_VM,
    > KVM_TDX_INIT_VCPU,
    > KVM_TDX_EXTEND_MEMORY,
    > + KVM_TDX_FINALIZE_VM,
    >
    > KVM_TDX_CMD_NR_MAX,
    > };
    > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
    > index 3cfba63a7762..6aff3f7e2488 100644
    > --- a/arch/x86/kvm/vmx/tdx.c
    > +++ b/arch/x86/kvm/vmx/tdx.c
    > @@ -1400,6 +1400,24 @@ static int tdx_extend_memory(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
    > return ret;
    > }
    >
    > +static int tdx_td_finalizemr(struct kvm *kvm)
    > +{
    > + struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
    > + u64 err;
    > +
    > + if (!is_hkid_assigned(kvm_tdx) || is_td_finalized(kvm_tdx))
    > + return -EINVAL;
    > +
    > + err = tdh_mr_finalize(kvm_tdx->tdr_pa);
    > + if (WARN_ON_ONCE(err)) {

    Is a failed SEAMCALL really something to WARN over?

    > + pr_tdx_error(TDH_MR_FINALIZE, err, NULL);

    As per Paolo, error code is not returned in struct kvm_tdx_cmd

    > + return -EIO;
    > + }
    > +
    > + kvm_tdx->finalized = true;
    > + return 0;
    > +}
    > +
    > int tdx_vm_ioctl(struct kvm *kvm, void __user *argp)
    > {
    > struct kvm_tdx_cmd tdx_cmd;
    > @@ -1422,6 +1440,9 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp)
    > case KVM_TDX_EXTEND_MEMORY:
    > r = tdx_extend_memory(kvm, &tdx_cmd);
    > break;
    > + case KVM_TDX_FINALIZE_VM:
    > + r = tdx_td_finalizemr(kvm);
    > + break;
    > default:
    > r = -EINVAL;
    > goto out;


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