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Re: [PATCH 4/6] tools/hvmloader: Use cpu_policy to determine APIC IDs
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 25 Mar 2024 18:00:34 +0100
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>
- Delivery-date: Mon, 25 Mar 2024 17:00:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.03.2024 09:52, Roger Pau Monné wrote:
> On Tue, Jan 09, 2024 at 03:38:32PM +0000, Alejandro Vallejo wrote:
>> As part of topology correction efforts, APIC IDs can no longer be derived
>> strictly through the vCPU ID alone. Bring in the machinery for policy
>> retrieval and parsing in order to generate the proper MADT table and wake
>> the appropriate CPUs.
>
> I'm kind of unsure about this last part of the sentence, as I see no
> waking of CPUs in hvmloader. Is this referring to something else?
>
> I'm kind of unsure about bringing the cpu_policy machinery to
> hvmloader.
I share this concern and ...
> Won't it be simpler to just pass the array of APIC IDs in
> hvm_info_table? The current size of this struct is 48bytes, and an
> array of 128 32bit integers would be an additional 512bytes.
>
> AFAICT there's plenty of room in hvm_info_table, it's
> positioned at 0x9f800, and there's unused space up to 0x9fc00, so 1024
> bytes of memory we could use.
>
> I know this doesn't give us much room for expansion if we want to bump
> past 128 vCPUs, but a more appropriate solution IMO would be to move
> ACPI table creation to the toolstack.
>
> It's possible I'm missing some aspects, so if this has been considered
> and rejected would be good to note in the commit message.
... it being at least clarified whether alternatives were considered
and why they cannot / should not be used.
Jan
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