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Bits 63-48 of the I/OAPIC Redirection Table Entry map directly to bits 19-4 of the address used in the resulting MSI cycle. Historically, the x86 MSI format only used the top 8 of those 16 bits as the destination APIC ID, and the "Extended Destination ID" in the lower 8 bits was unused. With interrupt remapping, the lowest bit of the Extended Destination ID (bit 48 of RTE, bit 4 of MSI address) is now used to indicate a remappable format MSI. A hypervisor can use the other 7 bits of the Extended Destination ID to permit guests to address up to 15 bits of APIC IDs, thus allowing 32768 vCPUs before having to expose a vIOMMU and interrupt remapping to the guest. No behavioural change in this patch, since nothing yet permits APIC IDs above 255 to be used with the non-IR I/OAPIC domain. [ tglx: Converted it to the cleaned up entry/msi_msg format and added commentry ] Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20201024213535.443185-32-dwmw2@infradead.org
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.