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


  • To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 17 Nov 2022 12:05:36 +0100
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  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 17 Nov 2022 11:05:56 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 17.11.2022 11:23, Roger Pau Monné wrote:
> On Thu, Nov 17, 2022 at 10:27:41AM +0100, Jan Beulich wrote:
>> On 16.11.2022 17:42, 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.
>>
>> Plus we should have passed through Local x2APIC NMI Structures then as
>> well.
> 
> Sadly this is not possible for PVH dom0, Linux will use the ACPI
> Processor UID as vCPU ID in hypercalls, so if the UIDs don't start at
> 0 and are sequential Linux will panic during boot because vCPU
> operations will fail.

Sure - I was merely hinting at the original attempt having been incomplete
(besides being flawed as per the description here).

Jan




 


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