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When translation is already enabled at boot (e.g. kdump), the vt-d driver
copies context tables from the previous kernel's root table. In scalable
mode, buses that only populate the upper root half (UCTP, devfn >= 0x80)
should be written to ctxt_tbls[tbl_idx + 1] through copy_context_table().
However, the current copy path always uses tbl[tbl_idx + 0] in this situa-
tion. Since idx wraps to 0 at devfn 0x80 due to a zeroed LCTP, new_ce for
LCTP will be NULL and keep pos equals to 0. Thus, UCTP entries will be co-
pied into tbl[tbl_idx + 0] instead of tbl[tbl_idx + 1], and written after-
wards to root_entry[bus].lo instead of .hi in copy_translation_tables().
In short, devices on bus 0x80 with devfn >= 0x80 fail DMA with fault 0x39,
which will break drivers running in kernels with translation pre-enabled.
This fixes NO_PASID DMAR faults for UCTP-only buses such as:
DMAR: [DMA Read NO_PASID] Request device [80:14.0] fault addr 0xe81759000
[fault reason 0x39] SM: Present bit in Root Entry is clear
For instance, this fault yielded to locking issues between systemd and
xHCI, blocking a system's reboot after a vmcore was captured with kdump:
systemd-udevd[246]: usb3: Worker [255] processing SEQNUM=2193 is taking a long time
dracut-initqueue[277]: Timed out while waiting for udev queue to empty.
systemd-udevd[246]: usb3: Worker [255] processing SEQNUM=2193 killed
systemd-udevd[246]: usb3: Worker [255] terminated by signal 9 (KILL).
...
kdump[569]: saving vmcore complete
...
systemd-shutdown[1]: Rebooting.
INFO: task kworker/0:1:11 blocked for more than 122 seconds.
Not tainted 7.0.0-clean #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/0:1 state:D stack:0 pid:11 tgid:11 ppid:2 task_flags:0x4208160 flags:0x00080000
Workqueue: usb_hub_wq hub_event
Call Trace:
<TASK>
__schedule+0x299/0x5c0
schedule+0x27/0x80
schedule_timeout+0xbd/0x100
__wait_for_common+0x97/0x1b0
? __pfx_schedule_timeout+0x10/0x10
xhci_alloc_dev+0x9e/0x2b0
usb_alloc_dev+0x7a/0x3b0
hub_port_connect+0x285/0x960
hub_port_connect_change+0x94/0x290
port_event+0x4bb/0x840
hub_event+0x141/0x460
process_one_work+0x196/0x390
worker_thread+0x1af/0x320
? __pfx_worker_thread+0x10/0x10
kthread+0xe3/0x120
? __pfx_kthread+0x10/0x10
ret_from_fork+0x199/0x260
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
INFO: task systemd-shutdow:1 blocked for more than 122 seconds.
Not tainted 7.0.0-clean #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:systemd-shutdow state:D stack:0 pid:1 tgid:1 ppid:0 task_flags:0x400100 flags:0x00080000
Call Trace:
<TASK>
__schedule+0x299/0x5c0
schedule+0x27/0x80
schedule_preempt_disabled+0x15/0x30
__mutex_lock.constprop.0+0x547/0xac0
device_shutdown+0xac/0x1b0
kernel_restart+0x3a/0x70
__do_sys_reboot+0x147/0x240
do_syscall_64+0x11b/0x6a0
? handle_mm_fault+0x110/0x350
? do_user_addr_fault+0x206/0x680
? irqentry_exit+0x7a/0x4d0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fe2958da917
RSP: 002b:00007ffc5c458618 EFLAGS: 00000206 ORIG_RAX: 00000000000000a9
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fe2958da917
RDX: 0000000001234567 RSI: 0000000028121969 RDI: 00000000fee1dead
RBP: 00007ffc5c458790 R08: 0000000000000069 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000000 R14: 00007ffc5c4588b8 R15: 0000000000000000
</TASK>
INFO: task systemd-shutdow:1 is blocked on a mutex likely owned by task kworker/0:1:11.
Fixes:
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History
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
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| sound | ||
| tools | ||
| usr | ||
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| .clang-format | ||
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| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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. 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