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0c7ffa32db
Implement the validation function which tells the core code whether parallel bringup is possible. The only condition for now is that the kernel does not run in an encrypted guest as these will trap the RDMSR via #VC, which cannot be handled at that point in early startup. There was an earlier variant for AMD-SEV which used the GHBC protocol for retrieving the APIC ID via CPUID, but there is no guarantee that the initial APIC ID in CPUID is the same as the real APIC ID. There is no enforcement from the secure firmware and the hypervisor can assign APIC IDs as it sees fit as long as the ACPI/MADT table is consistent with that assignment. Unfortunately there is no RDMSR GHCB protocol at the moment, so enabling AMD-SEV guests for parallel startup needs some more thought. Intel-TDX provides a secure RDMSR hypercall, but supporting that is outside the scope of this change. Fixup announce_cpu() as e.g. on Hyper-V CPU1 is the secondary sibling of CPU0, which makes the @cpu == 1 logic in announce_cpu() fall apart. [ mikelley: Reported the announce_cpu() fallout Originally-by: David Woodhouse <dwmw@amazon.co.uk> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Michael Kelley <mikelley@microsoft.com> Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name> Tested-by: Helge Deller <deller@gmx.de> # parisc Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck Link: https://lore.kernel.org/r/20230512205257.467571745@linutronix.de
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.