openvm_stark_backend/prover/

hal.rs

use std::sync::Arc;

use serde::{de::DeserializeOwned, Serialize};

use crate::{
    keygen::types::MultiStarkProvingKey,
    prover::{
        stacked_pcs::StackedPcsData, AirProvingContext, ColMajorMatrix, CommittedTraceData,
        CpuColMajorBackend, DeviceMultiStarkProvingKey, DeviceStarkProvingKey, ProvingContext,
    },
    StarkProtocolConfig,
};

pub trait MatrixDimensions {
    fn height(&self) -> usize;
    fn width(&self) -> usize;
}

/// Associated types needed by the prover, in the form of buffers and views,
/// specific to a specific hardware backend.
///
/// Memory allocation and copying is not handled by this trait.
pub trait ProverBackend {
    /// Extension field degree for the challenge field `Self::Challenge` over base field
    /// `Self::Val`.
    const CHALLENGE_EXT_DEGREE: u8;
    // ==== Host Types ====
    /// Base field type, on host.
    type Val: Copy + Send + Sync + Serialize + DeserializeOwned;
    /// Challenge field (extension field of base field), on host.
    type Challenge: Copy + Send + Sync + Serialize + DeserializeOwned;
    /// Single commitment on host.
    // Commitments are small in size and need to be transferred back to host to be included in
    // proof.
    type Commitment: Clone + Send + Sync + Serialize + DeserializeOwned;

    // ==== Device Types ====
    /// Single matrix buffer on device together with dimension metadata. Owning this means nothing
    /// else has a shared reference to the buffer.
    type Matrix: MatrixDimensions + Send + Sync;
    /// Backend specific type for any pre-computed data associated with a single AIR. For example,
    /// it may contain prover-specific precomputations based on the AIR constraints (but
    /// independent from any trace data).
    type OtherAirData: Send + Sync;
    /// Owned buffer for the preimage of a PCS commitment on device, together with any metadata
    /// necessary for computing opening proofs.
    ///
    /// For example, multiple buffers for LDE matrices, their trace domain sizes, and pointer to
    /// mixed merkle tree.
    type PcsData: Send + Sync;

    // ==== Metering Functions ====
    /// Per-row intermediate buffer size required to evaluate this AIR's constraints during
    /// batch constraints zerocheck round 0. Constant `0` (the default) means the backend does
    /// not track this; if all AIRs report `0`, memory metering falls back to the full round-0
    /// temporary-memory limit.
    fn constraint_eval_buffer_size(_pk: &DeviceStarkProvingKey<Self>) -> usize
    where
        Self: Sized,
    {
        0
    }
}

pub trait ProverDevice<PB: ProverBackend, TS>:
    TraceCommitter<PB> + MultiRapProver<PB, TS> + OpeningProver<PB, TS>
{
    type Error: 'static
        + std::error::Error
        + Send
        + Sync
        + From<<Self as TraceCommitter<PB>>::Error>
        + From<<Self as MultiRapProver<PB, TS>>::Error>
        + From<<Self as OpeningProver<PB, TS>>::Error>;

    /// Device-specific context (e.g., CUDA stream). Unit `()` for CPU devices.
    type DeviceCtx: Clone + Send + Sync;

    fn device_ctx(&self) -> &Self::DeviceCtx;
}

/// Provides functionality for committing to a batch of trace matrices, possibly of different
/// heights.
pub trait TraceCommitter<PB: ProverBackend> {
    type Error: std::fmt::Debug;
    fn commit(&self, traces: &[&PB::Matrix]) -> Result<(PB::Commitment, PB::PcsData), Self::Error>;
}

/// This trait is responsible for the proving steps that reduce AIR zerocheck constraints and
/// interaction consistency claims to polynomial opening claims.
///
/// This trait is _not_ responsible for committing to trace matrices or for checking polynomial
/// openings against PCS commitments.
pub trait MultiRapProver<PB: ProverBackend, TS> {
    /// The partial proof is the proof that the trace matrices satisfy all constraints assuming that
    /// certain polynomial opening claims are validated. In other words, it is a proof that reduces
    /// the constraint satisfaction claim to certain polynomial opening claims.
    type PartialProof: Clone + Send + Sync + Serialize + DeserializeOwned;
    /// Other artifacts of the proof (e.g., sampled randomness) that may be passed to later stages
    /// of the protocol.
    type Artifacts;

    type Error: std::fmt::Debug;

    fn prove_rap_constraints(
        &self,
        transcript: &mut TS,
        mpk: &DeviceMultiStarkProvingKey<PB>,
        ctx: &ProvingContext<PB>,
        common_main_pcs_data: &PB::PcsData,
    ) -> Result<(Self::PartialProof, Self::Artifacts), Self::Error>;
}

/// This trait is responsible for proving the evaluation claims of a collection of polynomials at a
/// collection of points. The opening point may be the same across polynomials. The polynomials may
/// be defined over different domains and are hence of "mixed" nature. The polynomials are already
/// committed and provided in their committed form.
pub trait OpeningProver<PB: ProverBackend, TS> {
    /// PCS opening proof on host. This should not be a reference.
    type OpeningProof: Clone + Send + Sync + Serialize + DeserializeOwned;
    type OpeningPoints;

    /// Computes the opening proof.
    /// The `common_main_pcs_data` is the `PcsData` for the collection of common main trace
    /// matrices. It is owned by the function and may be mutated.
    /// The `pre_cached_pcs_data_per_commit` is the `PcsData` for the preprocessed and cached trace
    /// matrices. These are specified by their `PcsData` per commitment.
    type Error: std::fmt::Debug;

    fn prove_openings(
        &self,
        transcript: &mut TS,
        mpk: &DeviceMultiStarkProvingKey<PB>,
        ctx: ProvingContext<PB>,
        common_main_pcs_data: PB::PcsData,
        points: Self::OpeningPoints,
    ) -> Result<Self::OpeningProof, Self::Error>;
}

/// Trait to manage data transport of prover types from host to device.
pub trait DeviceDataTransporter<SC, PB>
where
    SC: StarkProtocolConfig,
    PB: ProverBackend<Val = SC::F, Challenge = SC::EF, Commitment = SC::Digest>,
{
    /// Transport the proving key to the device, filtering for only the provided `air_ids`.
    fn transport_pk_to_device(
        &self,
        mpk: &MultiStarkProvingKey<SC>,
    ) -> DeviceMultiStarkProvingKey<PB>;

    fn transport_matrix_to_device(&self, matrix: &ColMajorMatrix<SC::F>) -> PB::Matrix;

    /// The `commitment` and `prover_data` are assumed to have been previously computed from the
    /// `trace`.
    fn transport_pcs_data_to_device(
        &self,
        pcs_data: &StackedPcsData<SC::F, SC::Digest>,
    ) -> PB::PcsData;

    fn transport_committed_trace_data_to_device(
        &self,
        committed_trace: &CommittedTraceData<CpuColMajorBackend<SC>>,
    ) -> CommittedTraceData<PB> {
        let trace = self.transport_matrix_to_device(&committed_trace.trace);
        let data = self.transport_pcs_data_to_device(committed_trace.data.as_ref());

        CommittedTraceData {
            commitment: committed_trace.commitment,
            trace,
            data: Arc::new(data),
        }
    }

    fn transport_proving_ctx_to_device(
        &self,
        ctx: &ProvingContext<CpuColMajorBackend<SC>>,
    ) -> ProvingContext<PB> {
        let per_trace = ctx
            .per_trace
            .iter()
            .map(|(air_idx, trace_ctx)| {
                let common_main = self.transport_matrix_to_device(&trace_ctx.common_main);
                let cached_mains = trace_ctx
                    .cached_mains
                    .iter()
                    .map(|cd| self.transport_committed_trace_data_to_device(cd))
                    .collect();
                let trace_ctx_gpu = AirProvingContext::new(
                    cached_mains,
                    common_main,
                    trace_ctx.public_values.clone(),
                );
                (*air_idx, trace_ctx_gpu)
            })
            .collect();
        ProvingContext::new(per_trace)
    }

    // ==================================================================================
    // Device-to-Host methods below should only be used for testing / debugging purposes.
    // ==================================================================================

    /// Transport a device matrix to host. This should only be used for testing / debugging
    /// purposes.
    fn transport_matrix_from_device_to_host(&self, matrix: &PB::Matrix) -> ColMajorMatrix<SC::F>;
}