---
id: pr-flash-attention-1604
repo: Dao-AILab/flash-attention
pr: 1604
title: Support hdimQK != hdimV backward
author: shcho1118
date: '2025-04-24'
url: https://github.com/Dao-AILab/flash-attention/pull/1604
source_category: upstream-code
architectures:
- sm90
tags:
- arch_pipeline
- attention_kv
- benchmark_test
- hopper
- norm_elementwise
- sm90
- tma
techniques:
- async-copy
- epilogue-fusion
- pipeline-stages
hardware_features:
- hopper
- tma
kernel_types:
- attention
- norm
- runtime
languages:
- cuda-cpp
captured_at: '2026-05-16'
status: merged
merge_sha: 37c816ab0d8fdfe90e8d50a756da8ef2b70ad2bc
inclusion_reason: 'Extract the architecture assumption first: SM target, TMA/WGMMA/tcgen path, cluster use, and pipeline stages.'
changed_paths:
- hopper/epilogue_bwd.hpp
- hopper/flash_api.cpp
- hopper/flash_attn_interface.py
- hopper/flash_bwd_launch_template.h
- hopper/mainloop_bwd_sm80.hpp
- hopper/mainloop_bwd_sm90_tma_gmma_ws.hpp
- hopper/test_flash_attn.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-1604
head_ref_oid: 69a84a3c7309668aaba7ba3d8dadd4884695d6b2
---
# Support hdimQK != hdimV backward

- Repository: `Dao-AILab/flash-attention`
- PR: [1604](https://github.com/Dao-AILab/flash-attention/pull/1604)
- Decision: `Extract the architecture assumption first: SM target, TMA/WGMMA/tcgen path, cluster use, and pipeline stages.`
- Reason: Extract the architecture assumption first: SM target, TMA/WGMMA/tcgen path, cluster use, and pipeline stages.

## Changed Paths

- `hopper/epilogue_bwd.hpp`
- `hopper/flash_api.cpp`
- `hopper/flash_attn_interface.py`
- `hopper/flash_bwd_launch_template.h`
- `hopper/mainloop_bwd_sm80.hpp`
- `hopper/mainloop_bwd_sm90_tma_gmma_ws.hpp`
- `hopper/test_flash_attn.py`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-1604`
