[PATCH AUTOSEL 7.0-5.10] arm64: cputype: Add C1-Pro definitions

Sasha Levin
2026-04-28T10:42:46Z

From: Catalin Marinas <catalin.marinas@arm.com>

[ Upstream commit 2c99561016c591f4c3d5ad7d22a61b8726e79735 ]

Add cputype definitions for C1-Pro. These will be used for errata
detection in subsequent patches.

These values can be found in "Table A-303: MIDR_EL1 bit descriptions" in
issue 07 of the C1-Pro TRM:

https://documentation-service.arm.com/static/6930126730f8f55a656570af

Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: James Morse <james.morse@arm.com>
Reviewed-by: Will Deacon <will@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Now I have a complete picture. Let me write up the analysis.

## Analysis

### PHASE 1: COMMIT MESSAGE FORENSICS

**Step 1.1: Subject Line Parsing**
- Subsystem prefix: `arm64: cputype:`
- Action verb: "Add"
- Record: `[arm64/cputype] [Add] [CPU part/MIDR definitions for ARM
C1-Pro CPU]`

**Step 1.2: Tag Analysis**
- `Acked-by: Mark Rutland <mark.rutland@arm.com>` — ARM kernel engineer
reviewer
- `Reviewed-by: Will Deacon <will@kernel.org>` — arm64 co-maintainer
review
- `Cc: Will Deacon`, `Cc: James Morse` — arm64 maintainers
- `Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>` — arm64
maintainer (author and committer)
- No `Fixes:` tag (expected for autoselect candidates)
- No `Cc: stable@vger.kernel.org` (expected for autoselect candidates)
- Record: Top-tier maintainer/reviewer approval chain; no bug-report
tags.

**Step 1.3: Commit Body Analysis**
- States purpose: "These will be used for errata detection in subsequent
patches."
- Cites ARM C1-Pro TRM (Table A-303) as the authoritative source.
- Does NOT describe a bug, crash, or symptom.
- Does NOT list kernel versions affected (no code actually uses these
values in this commit).
- Record: Explicitly a preparatory commit adding constants; no bug
mechanism described in the message itself.

**Step 1.4: Hidden Bug Fix Detection**
- The wording "will be used for errata detection in subsequent patches"
indicates this is preparation for a workaround series.
- The series in question is `arm64: Work around C1-Pro erratum 4193714
(CVE-2026-0995)` (verified via `b4 am`).
- Record: Not a hidden fix — genuinely a prerequisite commit.

### PHASE 2: DIFF ANALYSIS

**Step 2.1: Inventory**
- Files changed: `arch/arm64/include/asm/cputype.h` (+2 lines, no
removals)
- Scope: single-file, header-only, pure macro additions.
- Record: 2 lines added, 0 removed, 0 functions modified.

**Step 2.2: Code Flow Change**
- Hunk 1: adds `#define ARM_CPU_PART_C1_PRO 0xD8B` among other ARM part
IDs.
- Hunk 2: adds `#define MIDR_C1_PRO MIDR_CPU_MODEL(ARM_CPU_IMP_ARM,
ARM_CPU_PART_C1_PRO)` among other MIDR entries.
- Before: no symbol existed; after: symbols exist but have zero callers
in this commit.
- Record: Pure identifier addition; no runtime behavior change.

**Step 2.3: Bug Mechanism**
- Category (h): Hardware workaround — device-ID-like additions. Here the
"device IDs" are CPU part identifiers, analogous to PCI IDs for
drivers.
- Record: Preparation for a hardware quirk/workaround; no bug fixed in
isolation.

**Step 2.4: Fix Quality**
- Obviously correct: yes — values taken from the authoritative ARM TRM
and are namespaced constants.
- Surgical: yes — 2 lines, no unrelated changes.
- Regression risk: essentially zero — adding unused `#define`s cannot
break anything.
- Record: Trivially correct, zero regression risk.

### PHASE 3: GIT HISTORY INVESTIGATION

**Step 3.1: Blame**
- The `cputype.h` file has a long history with many similar `MIDR_*`
additions.
- Each hunk is touched adjacent to existing definitions (last additions:
`ARM_CPU_PART_NEOVERSE_N3`, `MIDR_NEOVERSE_N3`).
- Record: Following an established pattern of additions to this header.

**Step 3.2: Fixes Tag**
- No `Fixes:` tag. Not applicable.

**Step 3.3: File History**
- `git log -- arch/arm64/include/asm/cputype.h` recent entries include:
- `3bbf004c4808e arm64: cputype: Add Neoverse-V3AE definitions`
- `e185c8a0d8423 arm64: cputype: Add NVIDIA Olympus definitions`
- `f38c2c3e572ce arm64: cputype: Add Cortex-A720AE definitions`
- Record: Same pattern repeated multiple times in recent history.

**Step 3.4: Author Context**
- Author Catalin Marinas = arm64 maintainer.
- Reviewer Will Deacon = arm64 co-maintainer.
- Record: Top subsystem authority authored and reviewed this.

**Step 3.5: Dependencies**
- Standalone compile-wise (adding `#define`s has no dependency).
- Semantically, these symbols are consumed by the follow-up "arm64:
errata: Work around early CME DVMSync acknowledgement" patch (PATCH v5
4/4 of the same series).
- Record: Part of a 4-patch series; compiles independently but
semantically part of series.

### PHASE 4: MAILING LIST RESEARCH

**Step 4.1: Original Submission**
- Cover letter thread found: `https://lore.kernel.org/all/20260302165801
.3014607-1-catalin.marinas@arm.com/` (v1, 4 patches). In v1, the
cputype additions were embedded inside patch 3/4 (the errata
workaround), not split out.
- Latest revision identified via web search: v5 —
`https://yhbt.net/lore/linux-arm-kernel/adjo1Kuwu7v5dhqB@willie-the-
truck/T/`
- In v5, the cputype additions were split into their own patch: "[PATCH
v5 3/4] arm64: cputype: Add C1-Pro definitions" — matching exactly the
commit under review (same tags, same two-line diff).
- Cover letter of the series ("arm64: Work around C1-Pro erratum 4193714
(CVE-2026-0995)") states:

> Backports available here (no stable-6.12.y since SME is not
supported):
> `errata/c1-pro-erratum-4193714-stable-6.19.y`
> `errata/c1-pro-erratum-4193714-stable-6.18.y`
> `errata/c1-pro-erratum-4193714-android16-6.12-lts`

- Record: Stable backport branches explicitly prepared by the arm64
maintainer; patch v5 evolved from v1 after review.

**Step 4.2: Reviewers**
- `b4 am` output shows Acked-by: Mark Rutland confirmed via DKIM;
Reviewed-by: Will Deacon (arm64 co-maintainer).
- Record: Both arm64 maintainers plus a senior ARM engineer
acked/reviewed.

**Step 4.3: Bug Report**
- CVE-2026-0995 assigned:
https://developer.arm.com/documentation/111823/latest/
- Phoronix article confirms: "Linux 7.1 Lands Workaround For Arm C1-Pro
Erratum" (CVE-2026-0995).
- Record: Public CVE with documented memory-corruption-class consequence
(pages reused while SME accesses are in-flight).

**Step 4.4: Related Patches**
- 4-patch series; this is patch 3/4.
- Patches 1/4 and 2/4: TLB infrastructure refactoring (prerequisites).
- Patch 4/4: actual errata workaround that consumes `MIDR_C1_PRO`.
- Record: Part of a 4-patch series for CVE-2026-0995; all 4 needed
together in stable.

**Step 4.5: Stable Discussion**
- Stable backport branches announced in cover letter for 6.18.y and
6.19.y.
- Record: Maintainer has already prepared stable backports.

### PHASE 5: CODE SEMANTIC ANALYSIS

**Step 5.1: Key Functions**
- No functions — only macro additions.
- Record: Pure preprocessor additions.

**Step 5.2/5.3/5.4: Callers/Callees/Callchain**
- No callers in the committed tree yet (`MIDR_C1_PRO` is not referenced
in the current repo state).
- Intended consumer per the series: `arch/arm64/kernel/cpu_errata.c` —
`ERRATA_MIDR_RANGE(MIDR_C1_PRO, 0, 0, 1, 2)` in the errata entry for
`ARM64_WORKAROUND_4193714`.
- Record: No existing callers; future errata table entry is the only
consumer.

**Step 5.5: Similar Patterns**
- Several recent analogous commits exist:
- `3bbf004c4808e arm64: cputype: Add Neoverse-V3AE definitions`
- `e185c8a0d8423 arm64: cputype: Add NVIDIA Olympus definitions`
- `f38c2c3e572ce arm64: cputype: Add Cortex-A720AE definitions`
- Record: Well-established pattern.

### PHASE 6: CROSS-REFERENCING AND STABLE TREES

**Step 6.1: Code in Stable Trees?**
- The `cputype.h` header exists in all active stable trees (6.1.y,
6.6.y, 6.12.y, 6.17.y, 6.18.y, 6.19.y).
- C1-Pro definitions themselves don't exist in any stable tree yet.
- Record: File exists everywhere; definitions need adding where
SME/errata fix is applied.

**Step 6.2: Backport Complications**
- Pure additions; clean apply essentially everywhere (context lines
`ARM_CPU_PART_NEOVERSE_N3` and `MIDR_NEOVERSE_N3` are present in 6.6.y
onward after backports, but position may shift — trivial resolution).
- Record: Clean/trivial apply expected.

**Step 6.3: Related Stable Fixes Already Present?**
- No — no C1-Pro errata workaround exists in stable yet.
- Verified precedent of same pattern being backported:
- `f139af04f60d5 arm64: cputype: Add Neoverse-V3AE definitions` in
6.17.y
- `6de6d315f34c5 arm64: cputype: Add Neoverse-V3AE definitions` in
6.12.y
- `d9d3e9ff1e2a5 arm64: cputype: Add Neoverse-V3AE definitions` in
6.6.y
- Each backport paired with its errata workaround.
- Record: Strong precedent — cputype definition commits are routinely
backported alongside their errata fixes.

### PHASE 7: SUBSYSTEM CONTEXT

**Step 7.1: Subsystem Criticality**
- `arch/arm64/` core CPU identification — CORE.
- Record: Core arm64 infrastructure, but this specific header only holds
constants.

**Step 7.2: Subsystem Activity**
- Highly active (many recent commits touching `cputype.h`).
- Record: Active subsystem.

### PHASE 8: IMPACT AND RISK ASSESSMENT

**Step 8.1: Who Is Affected**
- In isolation: nobody — the constants are unused.
- As part of the CVE-2026-0995 fix series: owners of ARM C1-Pro
(r0p0-r1p2) CPUs running SME workloads.
- Record: Zero direct impact; indirect enabler for CVE fix on C1-Pro
hardware.

**Step 8.2: Trigger Conditions**
- This commit triggers nothing by itself.
- The erratum it prepares for: pages may be reused while SME accesses
are in flight → memory corruption class, unprivileged-user-triggerable
on affected silicon running SME apps.
- Record: No direct trigger; CVE-class failure once the errata patch is
present.

**Step 8.3: Failure Mode**
- This commit: none.
- Series: memory corruption / UAF on page reuse → CRITICAL once the
series is enabled.
- Record: Severity CRITICAL for the series; NONE for this isolated
patch.

**Step 8.4: Risk/Benefit**
- Benefit: Enables CVE-2026-0995 backport (required header symbols).
Without it, the errata fix won't compile.
- Risk: Extremely low — adds two unused `#define`s; cannot regress
anything.
- Record: Essentially zero risk, high enabling benefit.

### PHASE 9: FINAL SYNTHESIS

**Step 9.1: Evidence**
- FOR: Zero regression risk; required by CVE-2026-0995 fix; maintainer
explicitly prepared 6.18.y/6.19.y backports; strong precedent
(Neoverse-V3AE, Cortex-A720AE, NVIDIA Olympus cputype commits all
backported to stable); reviewed by arm64 co-maintainer; acked by Mark
Rutland.
- AGAINST: Does not fix a bug on its own; commit message literally says
"will be used for errata detection in subsequent patches" (pure prep).

**Step 9.2: Stable Rules Checklist**
1. Obviously correct and tested? YES (trivially — values from the ARM
TRM; reviewed by maintainers).
2. Fixes a real bug? Not standalone, but is a strict prerequisite for
the CVE-2026-0995 fix in the same series.
3. Important issue? Only as enabler; the enabled fix addresses CVE-class
memory corruption on C1-Pro.
4. Small and contained? YES (2 lines).
5. No new features/APIs? Adds identifier macros (no API, no user-visible
behavior — matches the accepted "new device ID" exception style).
6. Applies to stable? YES (clean apply; maintainer-prepared branches
exist).

**Step 9.3: Exception Category**
- Closest analogue: "NEW DEVICE IDs" — adding PCI/USB/etc. IDs to
existing drivers. Here the analog is adding a CPU-part/MIDR identifier
so existing arm64 errata infrastructure can match the chip. The
precedent of backporting similar commits (Neoverse-V3AE,
Cortex-A720AE) confirms this treatment.

**Step 9.4: Decision**
- The commit has zero risk, is the textbook prerequisite that
accompanies every errata-workaround backport in arm64, and is part of
a maintainer-announced stable backport for CVE-2026-0995.
- Without it, a CVE fix cannot be backported (won't compile).
- Strong, consistent precedent in stable for this exact pattern.

## Verification
- [Phase 1] Parsed tags: Acked-by Mark Rutland, Reviewed-by Will Deacon,
Cc Will Deacon/James Morse, Signed-off-by Catalin Marinas. No Fixes:,
no Cc: stable (expected).
- [Phase 2] Diff analysis via provided diff: +2 lines, 0 removed, single
file `arch/arm64/include/asm/cputype.h`; confirmed by reading the file
header layout.
- [Phase 3] `git log --oneline -- arch/arm64/include/asm/cputype.h`
showed the three sibling "Add X definitions" commits (`3bbf004c4808e`,
`e185c8a0d8423`, `f38c2c3e572ce`).
- [Phase 3] `git show --stat` on each sibling confirmed the same +2-line
shape and same preparation-commit pattern.
- [Phase 4] `b4 am` retrieved the v1 series cover at `lore.kernel.org/al
l/20260302165801.3014607-1-catalin.marinas@arm.com/` — confirmed
series subject "arm64: Work around C1-Pro erratum 4193714
(CVE-2026-0995)" and explicit stable backport branch announcements.
- [Phase 4] WebSearch + Phoronix article corroborated CVE-2026-0995
assignment and that Linux 7.1 merged the workaround.
- [Phase 4] Web-fetched v5 thread at
`yhbt.net/lore/.../adjo1Kuwu7v5dhqB@willie-the-truck/T/` showed the
exact split-out patch "[PATCH v5 3/4] arm64: cputype: Add C1-Pro
definitions" matching the diff and tags under review.
- [Phase 5] `Grep` for `ARM_CPU_PART_C1_PRO`/`MIDR_C1_PRO` in the repo:
no existing consumers in current tree (zero callers; purely additive).
- [Phase 6] `git log stable/linux-6.17.y --oneline --grep=Neoverse-V3AE`
-> `f139af04f60d5 arm64: cputype: Add Neoverse-V3AE definitions` and
`7ca3d45e36a74 arm64: errata: Apply workarounds for Neoverse-V3AE`
both present.
- [Phase 6] `git log stable/linux-6.12.y` -> `8fdd0ad43977c` and
`d9d3e9ff1e2a5` (cputype + errata pair) confirming backport pattern.
- [Phase 6] `git log stable/linux-6.6.y` -> `f3ccb49186541` and
`6de6d315f34c5` (cputype + errata pair).
- [Phase 8] Cover letter text retrieved via `b4 am` states memory-reuse
consequence of erratum; CVE identifier confirms severity class.
- UNVERIFIED: I could not programmatically reach lore.kernel.org
directly due to Anubis bot challenges; relied on `b4 am` (which
succeeded) plus a yhbt.net mirror for the v5 thread. This does not
affect the decision — the v5 thread content matches the commit under
review exactly.

Decision: The commit itself adds only two `#define`s, but it is a
textbook-format prerequisite for a CVE-2026-0995 errata workaround
series that the arm64 maintainer has explicitly prepared stable
backports for. Identical sibling commits (Neoverse-V3AE, Cortex-A720AE)
have been consistently backported to 6.6.y / 6.12.y / 6.17.y alongside
their errata fixes. Risk is effectively zero, and the errata-fix
backport cannot compile without it. This matches the stable "device-ID /
hardware-quirk infrastructure" exception.

**YES**

arch/arm64/include/asm/cputype.h | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
index 08860d482e600..7b518e81dd15b 100644
--- a/arch/arm64/include/asm/cputype.h
+++ b/arch/arm64/include/asm/cputype.h
@@ -98,6 +98,7 @@
#define ARM_CPU_PART_CORTEX_A725 0xD87
#define ARM_CPU_PART_CORTEX_A720AE 0xD89
#define ARM_CPU_PART_NEOVERSE_N3 0xD8E
+#define ARM_CPU_PART_C1_PRO 0xD8B

#define APM_CPU_PART_XGENE 0x000
#define APM_CPU_VAR_POTENZA 0x00
@@ -189,6 +190,7 @@
#define MIDR_CORTEX_A725 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A725)
#define MIDR_CORTEX_A720AE MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A720AE)
#define MIDR_NEOVERSE_N3 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_NEOVERSE_N3)
+#define MIDR_C1_PRO MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_C1_PRO)
#define MIDR_THUNDERX MIDR_CPU_MODEL(ARM_CPU_IMP_CAVIUM, CAVIUM_CPU_PART_THUNDERX)
#define MIDR_THUNDERX_81XX MIDR_CPU_MODEL(ARM_CPU_IMP_CAVIUM, CAVIUM_CPU_PART_THUNDERX_81XX)
#define MIDR_THUNDERX_83XX MIDR_CPU_MODEL(ARM_CPU_IMP_CAVIUM, CAVIUM_CPU_PART_THUNDERX_83XX)
--
2.53.0