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26505e1b5b
Red Hat is seeing multiple reports of Windows memory corruptions (and consequent BSODs) with hv-tlbflush=on, on AMD processors only. The crashes, while extremely rare, happen even with a stock configuration, but with Driver Verifier enabled they can be detected after approximately 200 VM hours. In particular, Alexander Lougovski measured the following: - on AMD Turin, 15 crashes in 3300 VM hours - on AMD Milan, 2 crashes in 500 VM hours (there are fewer hours here due to the host being smaller) - on Intel Sapphire Rapids, 0 crashes in 8000 VM hours - on AMD Turin with full TLB flush (not exactly this patch but similar), no crashes in ~2 weeks of run time which should also be ~7000 VM hours For Turin, the microcode version was 0x0b002162, which (assuming this is the same issue) should not be affected by the problem listed in https://knowledge.broadcom.com/external/article/419026/bsod-on-virtual-machines-running-on-amd.html; on the other hand that problem should not apply to earlier processors. AMD has not provided any information or analysis yet, and when we asked we didn't know yet that it reproduced on Milan as well. As to the workload, Alexander threw more or less everything at the same time at the VM: - a full Windows Defender scan every 30 minutes - a disk I/O job - a loop doing repeated mmap of system files (mostly to hope that it triggers some consistency check in the Windows memory manager) - SQL Express 2022 + StressDB (1.6M rows), with the host doing queries (75% write/25% read) via sqlcmd Driver Verifier is able to detect BSODs more or less at the same time as the pages are freed. They mostly happen in the Windows Defender filter driver, but occasionally also in the networking stack (e.g., afd.sys) or elsewhere in the filesystem stack (e.g., fltmgr.sys). The flush is issued from kvm_hv_vcpu_flush_tlb(), which receives the cross-CPU requests from the Hyper-V TLB flush hypercalls via a kfifo and is invoked by the KVM_REQ_HV_TLB_FLUSH request. The mechanism is the same for both Intel and AMD, and the handler for both vendors is a simple INVVPID(ADDR)/INVLPGA instruction. Because the request is handled on the destination CPU, there is a question of what happens if the VM is migrated across physical CPUs. In that case, the INVLPGA instruction would use a stale svm->vmcb->control.asid; but if anything that might do an *unnecessary* flush (on an asid that's being used for another VM) and then pre_svm_run() would force a full TLB rebuild. So, for lack of better ideas, this patch forces a full ASID bump in svm_flush_tlb_gva(). To avoid paying the price on Intel and also to avoid unnecessary loops on AMD, the flush_tlb_gva op now returns whether it did a full flush or not; kvm_hv_vcpu_flush_tlb() takes note and exits its loops immediately. While there is an obvious performance impact, about half of the benefit from Hyper-V tlbflush is preserved (10% vs. 20% on the SQL Server workload). kvm_mmu_invalidate_addr() is the only other caller of the flush_tlb_gva op. The change would have a performance impact on every intercepted INVLPG and, for nested SVM, on every L1 INVLPGA. For INVLPGA specifically, this covers the same suspected issue but for nested hypervisors, so it is correct to apply the workaround; for INVLPG on shadow paging, instead, the impact would be stronger and, due to lack of data, for now the use of INVLPGA is left in place in svm_flush_tlb_gva(). Analyzed-by: Vitaly Kuznetsov <vkuznets@redhat.com> Analyzed-by: Alexander Lougovski <alougovs@redhat.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