Claude review: drm/msm: Add PERFCNTR_CONFIG ioctl

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

Overall Series Review

Subject: drm/msm: Add PERFCNTR_CONFIG ioctl
Author: Rob Clark <robin.clark@oss.qualcomm.com>
Patches: 32
Reviewed: 2026-04-23T09:13:13.309094

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This is a 13-patch series from Rob Clark adding a new `PERFCNTR_CONFIG` ioctl to the MSM DRM driver. The series removes the old debugfs-based performance counter infrastructure and replaces it with a proper ioctl-based system supporting two modes: (1) global counter collection via an fd-based stream (requires `perfmon_capable()`), and (2) per-context counter reservation for local (within `GEM_SUBMIT`) counter collection. The design is well thought out -- global counters allocate from highest to lowest to avoid conflicts with old userspace, the stream fd model is clean, and the UABI is reasonably future-proof via `group_stride`.

However, there are several bugs that need fixing before merging, including a **critical loop variable typo** that can cause an infinite loop/ringbuffer corruption, a **stack buffer overflow** from unchecked `copy_from_user` size, and **NULL pointer dereferences** on GPUs without perfcntr support.

Overall the architecture is sound. The series needs a respin to fix the bugs identified below.

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