---
id: pr-flash-attention-2194
repo: Dao-AILab/flash-attention
pr: 2194
title: '[Cute, SM90] fix fwd varlen Cute implementation bug for H100'
author: KareemMusleh
date: '2026-01-20'
url: https://github.com/Dao-AILab/flash-attention/pull/2194
source_category: upstream-code
architectures:
- sm90
tags:
- sm90
techniques: []
hardware_features:
- hopper
kernel_types:
- attention
languages:
- cute-dsl
captured_at: '2026-05-16'
status: merged
merge_sha: 04e6ee1fb54f756e6f788e6b3962a7503c985394
inclusion_reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.
changed_paths:
- flash_attn/cute/flash_bwd.py
- flash_attn/cute/flash_bwd_sm90.py
- flash_attn/cute/flash_fwd.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-2194
head_ref_oid: 7ea993cf68bc116aeb3074148eefa8914165b56e
---
# [Cute, SM90] fix fwd varlen Cute implementation bug for H100

- Repository: `Dao-AILab/flash-attention`
- PR: [2194](https://github.com/Dao-AILab/flash-attention/pull/2194)
- Decision: `Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.`
- Reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.

## Changed Paths

- `flash_attn/cute/flash_bwd.py`
- `flash_attn/cute/flash_bwd_sm90.py`
- `flash_attn/cute/flash_fwd.py`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-2194`
