mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-16 02:01:18 -04:00
d7396a72ea
SCTLR_EL2.EIS and SCTLR_EL2.EOS control whether exception entry and
exit at EL2 are Context Synchronisation Events (CSEs). Per ARM DDI
0487 M.b D24.2.175 (p. D24-9754):
- !FEAT_ExS: the bit is RES1, so the entry/exit is unconditionally
a CSE.
- FEAT_ExS: the reset value is architecturally UNKNOWN; software
must set the bit to make the entry/exit a CSE.
INIT_SCTLR_EL2_MMU_ON in arch/arm64/include/asm/sysreg.h sets neither
bit. KVM/arm64 hot paths rely on ERET from EL2 being a CSE, and on
synchronous EL1->EL2 entry being a CSE, to elide explicit ISBs after
MSRs to context-switching system registers (HCR_EL2, ZCR_EL2,
ptrauth keys, etc.). On FEAT_ExS hardware those reliances are not
architecturally backed unless EOS=1 (and, for entry, EIS=1).
Until commit 0a35bd285f ("arm64: Convert SCTLR_EL2 to sysreg
infrastructure"), SCTLR_EL2_RES1 was a hand-rolled mask that
included BIT(11) (EOS) and BIT(22) (EIS), so INIT_SCTLR_EL2_MMU_ON
was setting both unconditionally. The conversion made
SCTLR_EL2_RES1 auto-generated; because the sysreg tooling only
models unconditionally-RES1 fields and EIS/EOS are RES1 only when
FEAT_ExS is absent, the auto-generated mask is UL(0). The seven
other bits dropped from the old mask (positions 4, 5, 16, 18, 23,
28, 29) are unconditionally RES1 in the E2H=0 SCTLR_EL2 layout per
DDI 0487 M.b D24.2.175, so dropping them is harmless. EIS and EOS
are the only bits whose semantics changed for FEAT_ExS hardware
and where the kernel relies on the value being 1.
Make the guarantee explicit: include SCTLR_ELx_EIS | SCTLR_ELx_EOS in
INIT_SCTLR_EL2_MMU_ON so that EL2 exception entry and exit are
unconditionally CSEs regardless of whether FEAT_ExS is implemented.
This matches the pairing in arch/arm64/kvm/config.c which treats EIS
and EOS together as RES1 under !FEAT_ExS.
Fixes: 0a35bd285f ("arm64: Convert SCTLR_EL2 to sysreg infrastructure")
Reviewed-by: Yuan Yao <yaoyuan@linux.alibaba.com>
Assisted-by: Gemini:gemini-3.1-pro review-prompts
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260501112149.2824881-2-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst