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 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 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
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FEAT_TME has been dropped from the architecture. Retrospectively.
I'm sure someone is crying somewhere, but most of us won't.
Clean-up time.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-18-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Now that we embed the RESx bits in the register description, it becomes
easier to deal with registers that are simply not valid, as their
existence is not satisfied by the configuration (SCTLR2_ELx without
FEAT_SCTLR2, for example). Such registers essentially become RES0 for
any bit that wasn't already advertised as RESx.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-17-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
We have now killed every occurrences of FIXED_VALUE, and we can therefore
drop the whole infrastructure. Good riddance.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-16-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Now that we can link the RESx behaviour with the value of HCR_EL2.E2H,
we can trivially express the tautological constraint that makes E2H
a reserved value at all times.
Fun, isn't it?
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-15-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Instead of hacking the RES1 bits at runtime, move them into the
register descriptors. This makes it significantly nicer.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-14-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
"Thanks" to VHE, SCTLR_EL2 radically changes shape depending on the
value of HCR_EL2.E2H, as a lot of the bits that didn't have much
meaning with E2H=0 start impacting EL0 with E2H=1.
This has a direct impact on the RESx behaviour of these bits, and
we need a way to express them.
For this purpose, introduce two new constaints that, when the
controlling feature is not present, force the field to RES1 depending
on the value of E2H. Note that RES0 is still implicit,
This allows diverging RESx values depending on the value of E2H,
something that is required by a bunch of SCTLR_EL2 bits.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-13-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
A bunch of EL2 configuration are very similar to their EL1 counterpart,
with the added constraint that HCR_EL2.E2H being 1.
For us, this means HCR_EL2.E2H being RES1, which is something we can
statically evaluate.
Add a REQUIRES_E2H1 constraint, which allows us to express conditions
in a much simpler way (without extra code). Existing occurrences are
converted, before we add a lot more.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-12-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
The FIXED_VALUE qualifier (mostly used for HCR_EL2) is pointlessly
complicated, as it tries to piggy-back on the previous RES0 handling
while being done in a different phase, on different data.
Instead, make it an integral part of the RESx computation, and allow
it to directly set RESx bits. This is much easier to understand.
It also paves the way for some additional changes to that will allow
the full removal of the FIXED_VALUE handling.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-11-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Now that we have the AS_RES1 constraint, it becomes trivial to express
the HCR_EL2.RW behaviour.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-10-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
A bunch of SCTLR_EL1 bits must be set to RES1 when the controlling
feature is not present. Add the AS_RES1 qualifier where needed.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-9-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
So far, when a bit field is tied to an unsupported feature, we set
it as RES0. This is almost correct, but there are a few exceptions
where the bits become RES1.
Add a AS_RES1 qualifier that instruct the RESx computing code to
simply do that.
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-8-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
The FGT registers have their computed RESx bits stashed in specific
descriptors, which we can easily use when computing the masks used
for the guest.
This removes a bit of boilerplate code.
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-7-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Add a new helper to retrieve the RESx values for a given system
register, and use it for the runtime sanitisation.
This results in slightly better code generation for a fairly hot
path in the hypervisor, and additionally covers all sanitised
registers in all conditions, not just the VNCR-based ones.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-6-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
We have so far mostly tracked RES0 bits, but only made a few attempts
at being just as strict for RES1 bits (probably because they are both
rarer and harder to handle).
Start scratching the surface by introducing a data structure tracking
RES0 and RES1 bits at the same time.
Note that contrary to the usual idiom, this structure is mostly passed
around by value -- the ABI handles it nicely, and the resulting code is
much nicer.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-5-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Computing the FGU bits is made oddly complicated, as we use the RES0
helper instead of using a specific abstraction.
Introduce such an abstraction, which is going to make things significantly
simpler in the future.
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-4-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
We already have specific constraints for SCTLR_EL1.{EE,E0E}, and
making them depend on FEAT_AA64EL1 is just buggy.
Fixes: 6bd4a274b026e ("KVM: arm64: Convert SCTLR_EL1 to config-driven sanitisation")
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202184329.2724080-3-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>