On Wed, Oct 07 2020 at 13:20, David Woodhouse wrote:
> From: David Woodhouse <d...@amazon.co.uk>
>
> The IOAPIC Redirection Table Entries contain an 8-bit Extended
> Destination ID field which maps to bits 11-4 of the MSI address.
>
> The lowest bit is used to indicate remappable format, when interrupt
> remapping is in use. A hypervisor can use the other 7 bits 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 IOAPIC domain. Except for the case
> where IR is enabled but there are IOAPICs which aren't in the scope of
> any IOMMU, which is totally hosed anyway and needs fixing independently
> of this change.
Again: IOAPICs which are not covered by IR are detected and prevent IR
enablement which makes the above a fairy tale. Changelogs are about
facts.
> diff --git a/arch/x86/include/asm/io_apic.h b/arch/x86/include/asm/io_apic.h
> index a1a26f6d3aa4..e65a0b7379d0 100644
> --- a/arch/x86/include/asm/io_apic.h
> +++ b/arch/x86/include/asm/io_apic.h
> @@ -78,7 +78,8 @@ struct IO_APIC_route_entry {
> mask : 1, /* 0: enabled, 1: disabled */
> __reserved_2 : 15;
>
> - __u32 __reserved_3 : 24,
> + __u32 __reserved_3 : 17,
> + ext_dest : 7,
This wants to be explicitely named 'virt_ext_dest'.
Thanks,
tglx
