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Re: [PATCH 1/2] x86/apic: Get rid of get_physical_broadcast()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 1 Sep 2025 10:33:27 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 01 Sep 2025 08:33:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 29.08.2025 18:17, Andrew Cooper wrote:
> This is a port of Linux commit 517234446c1a ("x86/apic: Get rid of
> get_physical_broadcast()") to Xen. Thomas Gleixner notes:
>
> There is no point for this function. The only case where this is used is
> when there is no XAPIC available, which means the broadcast address is 0xF.
>
> In Linux, users of get_physical_broadcast() have already been hidden behind
> CONFIG_X86_32 suggesting we can drop all of this, but that's a task for some
> other time.
>
> In Xen as with Linux, setup_ioapic_ids_from_mpc() and io_apic_get_unique_id()
> are only called in pre-xAPIC cases, so can use a broadcast ID of 0xf. The
> only other user is __print_IO_APIC() for diagnostics, which can simply drop
> the check.
For setup_ioapic_ids_from_mpc() in Linux that's partly because it gained an
Intel && !APIC_XAPIC() check which we don't have. Without that extra bit of
data it's not quite obvious, as the check right now is solely "!acpi_ioapic".
(Which iirc we said we would want to get rid of as well.)
The non-Intel pre-xAPIC case is left somewhat unclear there, though.
> No functional change.
>
> Link: https://lore.kernel.org/r/20240212154639.057209154@xxxxxxxxxxxxx
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Irrespective of the above:
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
Jan
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