Claude review: dma-buf: heaps: system: add an option to allocate explicitly decrypted memory

[Claude Code Review Bot <claude-review@example.com>]

Overall Series Review

Subject: dma-buf: heaps: system: add an option to allocate
 explicitly decrypted memory
Author: Jiri Pirko <jiri@resnulli.us>
Patches: 17
Reviewed: 2026-02-11T16:59:17.557899

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This patch series introduces support for explicitly decrypted memory allocations in dma-buf system heaps for confidential computing (CoCo) environments (AMD SEV, Intel TDX). While the technical implementation appears sound in addressing a real problem, **the series has fundamental design issues that require revision before acceptance**.

### High-Level Assessment

**Problem Statement**: Valid and important. CoCo VMs need a way to allocate decrypted memory that can be:
- Shared across multiple DMA devices
- Mapped to userspace
- Used with pin_user_pages() (critical for RDMA)

**Approach Issues**:
1. **PATCH 4 violates dma-buf heaps design philosophy** - Using heap-specific flags contradicts the original design intent that heap flags should be generic across heaps
2. **Maintainer feedback indicates rejection** - John Stultz (original dma-buf heaps author) explicitly stated this approach recreates the ION driver problems they tried to avoid
3. **Author has agreed to change approach** - Will use separate heap name ("system_cc_decrypted") instead of flags

**Build Quality**: Failed on s390 architecture due to missing `set_memory_decrypted()`/`set_memory_encrypted()` stubs.

### Recommendation

**Do NOT merge in current form**. The series requires:
1. Remove PATCH 4 entirely (per-heap flag validation)
2. Redesign PATCH 5 to create a separate heap instead of using flags
3. Add architecture-specific guards or stubs for s390 and other architectures
4. Consider security implications for existing heaps on CoCo systems

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Generated by Claude Code Patch Reviewer