Re: [PATCH] x86/pvh: do not forward MADT Local APIC NMI structures to dom0

[Andrew Cooper <Andrew.Cooper3@citrix.com>]

On 16/11/2022 16:42, Roger Pau Monne wrote:
> Currently Xen will passthrough any Local APIC NMI Structure found in
> the native ACPI MADT table to a PVH dom0.  This is wrong because PVH
> doesn't have access to the physical local APIC, and instead gets an
> emulated local APIC by Xen, that doesn't have the LINT0 or LINT1
> pins wired to anything.  Furthermore the ACPI Processor UIDs used in
> the APIC NMI Structures are likely to not match the ones generated by
> Xen for the Local x2APIC Structures, creating confusion to dom0.
>
> Fix this by removing the logic to passthrough the Local APIC NMI
> Structure for PVH dom0.
>
> Fixes: 1d74282c45 ('x86: setup PVHv2 Dom0 ACPI tables')
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>

Yeah, that was never going to work correctly.

That said, I'm not certain we can get away with discarding them either. 
Some systems really do use ExtINT in IO-APIC entries, and dom0 is
capable of configuring this if it thinks it wants virtual wire mode.

Is dom0 likely to get more or less confused with the LAPIC not
defaulting to regular x86 norms?  (The answer to this question is
whether we should fake up up an NMI structure for each vCPU.)

~Andrew