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Paolo Bonzini ea8bc95fbb KVM nested SVM changes for 7.1 (with one common x86 fix)
- To minimize the probability of corrupting guest state, defer KVM's
    non-architectural delivery of exception payloads (e.g. CR2 and DR6) until
    consumption of the payload is imminent, and force delivery of the payload
    in all paths where userspace saves relevant state.
 
  - Use vcpu->arch.cr2 when updating vmcb12's CR2 on nested #VMEXIT to fix a
    bug where L2's CR2 can get corrupted after a save/restore, e.g. if the VM
    is migrated while L2 is faulting in memory.
 
  - Fix a class of nSVM bugs where some fields written by the CPU are not
    synchronized from vmcb02 to cached vmcb12 after VMRUN, and so are not
    up-to-date when saved by KVM_GET_NESTED_STATE.
 
  - Fix a class of bugs where the ordering between KVM_SET_NESTED_STATE and
    KVM_SET_{S}REGS could cause vmcb02 to be incorrectly initialized after
    save+restore.
 
  - Add a variety of missing nSVM consistency checks.
 
  - Fix several bugs where KVM failed to correctly update VMCB fields on nested
    #VMEXIT.
 
  - Fix several bugs where KVM failed to correctly synthesize #UD or #GP for
    SVM-related instructions.
 
  - Add support for save+restore of virtualized LBRs (on SVM).
 
  - Refactor various helpers and macros to improve clarity and (hopefully) make
    the code easier to maintain.
 
  - Aggressively sanitize fields when copying from vmcb12 to guard against
    unintentionally allowing L1 to utilize yet-to-be-defined features.
 
  - Fix several bugs where KVM botched rAX legality checks when emulating SVM
    instructions.  Note, KVM is still flawed in that KVM doesn't address size
    prefix overrides for 64-bit guests; this should probably be documented as a
    KVM erratum.
 
  - Fail emulation of VMRUN/VMLOAD/VMSAVE if mapping vmcb12 fails instead of
    somewhat arbitrarily synthesizing #GP (i.e. don't bastardize AMD's already-
    sketchy behavior of generating #GP if for "unsupported" addresses).
 
  - Cache all used vmcb12 fields to further harden against TOCTOU bugs.
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Merge tag 'kvm-x86-nested-7.1' of https://github.com/kvm-x86/linux into HEAD

KVM nested SVM changes for 7.1 (with one common x86 fix)

 - To minimize the probability of corrupting guest state, defer KVM's
   non-architectural delivery of exception payloads (e.g. CR2 and DR6) until
   consumption of the payload is imminent, and force delivery of the payload
   in all paths where userspace saves relevant state.

 - Use vcpu->arch.cr2 when updating vmcb12's CR2 on nested #VMEXIT to fix a
   bug where L2's CR2 can get corrupted after a save/restore, e.g. if the VM
   is migrated while L2 is faulting in memory.

 - Fix a class of nSVM bugs where some fields written by the CPU are not
   synchronized from vmcb02 to cached vmcb12 after VMRUN, and so are not
   up-to-date when saved by KVM_GET_NESTED_STATE.

 - Fix a class of bugs where the ordering between KVM_SET_NESTED_STATE and
   KVM_SET_{S}REGS could cause vmcb02 to be incorrectly initialized after
   save+restore.

 - Add a variety of missing nSVM consistency checks.

 - Fix several bugs where KVM failed to correctly update VMCB fields on nested
   #VMEXIT.

 - Fix several bugs where KVM failed to correctly synthesize #UD or #GP for
   SVM-related instructions.

 - Add support for save+restore of virtualized LBRs (on SVM).

 - Refactor various helpers and macros to improve clarity and (hopefully) make
   the code easier to maintain.

 - Aggressively sanitize fields when copying from vmcb12 to guard against
   unintentionally allowing L1 to utilize yet-to-be-defined features.

 - Fix several bugs where KVM botched rAX legality checks when emulating SVM
   instructions.  Note, KVM is still flawed in that KVM doesn't address size
   prefix overrides for 64-bit guests; this should probably be documented as a
   KVM erratum.

 - Fail emulation of VMRUN/VMLOAD/VMSAVE if mapping vmcb12 fails instead of
   somewhat arbitrarily synthesizing #GP (i.e. don't bastardize AMD's already-
   sketchy behavior of generating #GP if for "unsupported" addresses).

 - Cache all used vmcb12 fields to further harden against TOCTOU bugs.
History 2026-04-13 13:01:50 +02:00
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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