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When querying whether or not interrupts (IRQs) are allowed, check for a pending nested run _after_ checking whether or not interrupts are blocked. If L1 is running L2 _without_ nested_exit_on_intr(), i.e. if L1 IRQs can be blocked while running L2, and interrupts will indeed be blocked once the nested VM-Enter to L2 is completed, then KVM should treat interrupts as not being allowed. For injection, this avoids an unnecessary (forced) VM-Exit, as KVM can immediately request an IRQ window, instead of forcing an exit and _then_ requesting an IRQ window (because after the forced exit, KVM will see that interrupts are blocked). For non-injection usage, only kvm_vcpu_ready_for_interrupt_injection() is affected in practice. Barring KVM bugs or misbehaving userspace (at which point all architectural guarantees are off), kvm_vcpu_has_events() is unreachable when a nested run is pending. To reach kvm_vcpu_has_events(), kvm_vcpu_running() needs to return false, i.e. vcpu->arch.mp_state needs to be something other than RUNNABLE. If nested_run_pending is true, then mp_state *must* be RUNNABLE (again barring bugs or stupid userspace), because KVM shouldn't emulate VMRUN/VMLAUNCH/VMRESUME while the vCPU is !RUNNABLE. The one "near miss" is VMX's GUEST_ACTIVITY_STATE field, which allows L1 to put the vCPU into HLT or WFS as part of nested VMLAUNCH/VMRESUME. However, KVM clears nested_run_pending prior to calling kvm_emulate_halt_noskip() when putting L2 into HLT via GUEST_ACTIVITY_HLT, and also clears the flag before setting mp_state to INIT_RECEIVED. SVM has no equivalent to GUEST_ACTIVITY_STATE. I.e. the vCPU will always be runnable if a nested run is pending, and thus kvm_arch_vcpu_runnable() => kvm_vcpu_has_events() is effectively dead code, as is __kvm_emulate_halt() => kvm_vcpu_has_events(). Oh, and TDX doesn't support nested VMX. Similarly, kvm_can_do_async_pf() is unreachable as KVM shouldn't be faulting in memory with a pending nested VM-Enter. As for kvm_vcpu_ready_for_interrupt_injection(), KVM's current behavior of incorrectly treating interrupts as being allowed could result in KVM prematurely exiting to userspace to accept an ExtINT. But, KVM will still hold/block the ExtINT and request its own IRQ window. I.e. the net effect is more or less the same as the for-injection case, the unnecessary exit just happens at a different boundary. Signed-off-by: Sean Christopherson <seanjc@google.com> Message-ID: <20260613000329.732085-27-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
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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