fix(vmcall_raw): chunk send to honor VMCALL buffer MTU#918
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MichalTarnacki
approved these changes
Jun 30, 2026
kornelo
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Jun 30, 2026
A single TDG.VP.VMCALL<Service.MigTD.Send> can only carry up to the same MTU the receive side advertises (MAX_VMCALL_RAW_STREAM_MTU, 64KB). With policy_v2's peer-data blob now carrying the signed policy plus issuer chain (~180KB in practice), the rebinding pre-session body send fails with TdVmcallError::Other right after hello and the 8-byte data header succeed. Chunk on the send path so any single VMCALL payload stays at MAX_VMCALL_RAW_STREAM_MTU - 12 bytes (room for the GHCI 1.5 status+length header prepended by vmcall_raw_transport_enqueue). Loop inside VmcallRaw::send and keep returning buf.len(); this keeps the AsyncWrite contract intact for callers that don't loop on partial writes (rustls SecureChannel, SpdmDeviceIo). The wire framing is unchanged — the peer's receive loop already reassembles multiple packets in VmcallRaw::recv. Promote MAX_VMCALL_RAW_STREAM_MTU to pub(crate) and add explicit VMCALL_RAW_GHCI_HEADER_LEN / VMCALL_RAW_SEND_PAYLOAD_MTU consts so the overhead arithmetic is named at one site. Signed-off-by: Stanislaw Grams <stanislaw.grams@intel.com>
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A single TDG.VP.VMCALL<Service.MigTD.Send> can only carry up to the same MTU the receive side advertises (MAX_VMCALL_RAW_STREAM_MTU, 64KB). With policy_v2's peer-data blob now carrying the signed policy plus issuer chain (~180KB in practice), the rebinding pre-session body send fails with TdVmcallError::Other right after hello and the 8-byte data header succeed.
Chunk on the send path so any single VMCALL payload stays at MAX_VMCALL_RAW_STREAM_MTU - 12 bytes (room for the GHCI 1.5 status+length header prepended by vmcall_raw_transport_enqueue). Loop inside VmcallRaw::send and keep returning buf.len(); this keeps the AsyncWrite contract intact for callers that don't loop on partial writes (rustls SecureChannel, SpdmDeviceIo). The wire framing is unchanged — the peer's receive loop already reassembles multiple packets in VmcallRaw::recv.
Promote MAX_VMCALL_RAW_STREAM_MTU to pub(crate) and add explicit VMCALL_RAW_GHCI_HEADER_LEN / VMCALL_RAW_SEND_PAYLOAD_MTU consts so the overhead arithmetic is named at one site.