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Re: [PATCH 05/12] x86/io-apic: purge usage of logical mode
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 20 Nov 2025 13:18:37 +0000
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>
- Delivery-date: Thu, 20 Nov 2025 13:18:53 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20/11/2025 9:06 am, Roger Pau Monne wrote:
> The IO-APIC RTEs are unconditionally programmed with physical destination
> mode, and hence the field to set in the RTE is always physical_dest.
>
> Remove the mode parameter from SET_DEST() and take the opportunity to
> convert it into a function, there's no need for it to be a macro.
>
> This is a benign fix, because due to the endianness of x86 the start of the
> physical_dest and logical_dest fields on the RTE overlap.
RTEs do not have overlapping fields; it's Xen's abstraction of the
IO-APIC which is buggy.
For starters, Xen's IO_APIC_route_entry still only has a 4-bit
physical_dest field which hasn't been true since the Pentium 4 days.
This might explain some of the interrupt bugs we see.
~Andrew
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