Linux kernel for uConsole
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371b80447f
kexec can leave MMU registers set when booting into a new kernel,
the PIDR (Process Identification Register) in particular. The boot
sequence does not zero PIDR, so it only gets set when CPUs first
switch to a userspace processes (until then it's running a kernel
thread with effective PID = 0).
This leaves a window where a process table entry and page tables are
set up due to user processes running on other CPUs, that happen to
match with a stale PID. The CPU with that PID may cause speculative
accesses that address quadrant 0 (aka userspace addresses), which will
result in cached translations and PWC (Page Walk Cache) for that
process, on a CPU which is not in the mm_cpumask and so they will not
be invalidated properly.
The most common result is the kernel hanging in infinite page fault
loops soon after kexec (usually in schedule_tail, which is usually the
first non-speculative quadrant 0 access to a new PID) due to a stale
PWC. However being a stale translation error, it could result in
anything up to security and data corruption problems.
Fix this by zeroing out PIDR at boot and kexec.
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.