On Mon, 2020-10-05 at 15:18 +0100, David Woodhouse wrote: > The IOAPIC has an 'Extended Destination ID' field in its RTE, which maps > to bits 11-4 of the MSI address. Since those address bits fall within a > given 4KiB page they were historically non-trivial to use on real hardware. > > The Intel IOMMU uses the lowest bit to indicate a remappable format MSI, > and then the remaining 7 bits are part of the index. > > Where the remappable format bit isn't set, we can actually use the other > seven to allow external (IOAPIC and MSI) interrupts to reach up to 32768 > CPUs instead of just the 255 permitted on bare metal. > > Signed-off-by: David Woodhouse <d...@amazon.co.uk>
Corresponding kernel patch at https://patchwork.kernel.org/patch/11820535/
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