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On pre-r6 systems with the MT ASE the CPS SMP code included checks to halt the VPE running mips_cps_boot_vpes() if its bit in the struct core_boot_config vpe_mask field is clear. This was largely done in order to allow us to start arbitrary VPEs within a core despite the fact that hardware is typically configured to run only VPE0 after powering up a core. VPE0 would start the desired other VPEs, halt itself, and the fact that VPE0 started would be largely hidden & irrelevant. In MIPSr6 multithreading we have control over which VPs start executing when a core powers up via the cores CPC registers accessed remotely through the redirect block. For this reason the MIPSr6 multithreading path in mips_cps_boot_vpes() hasn't bothered up until now to handle halting the VP running it. However it is possible to power up cores entirely in hardware by using a pwr_up pin associated with the core. Unfortunately some systems wire this pin to a logic 1, which means that it is possible for a core to power up at a point that software doesn't expect. The result is that we generally go execute the kernel on a CPU that ought not to be running & the results can be unpredictable. Handle this case by stopping VPs that we don't expect to be running in mips_cps_boot_vpes() - with this change even if a core powers up it will do nothing useful & all VPs within it will stop running before they proceed to run general kernel code & do any damage. Ideally we would produce some sort of warning here, but given the stage of core bringup this happens at that would be non-trivial. We also will only hit this if a core starts up after being offlined via hotplug, and when that happens we will already produce a warning that the CPU didn't power down in cps_cpu_die() which seems sufficient. Signed-off-by: Paul Burton <paul.burton@imgtec.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/16198/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
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.