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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 13:12:20 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 01 Sep 2025 11:12:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 01.09.2025 13:03, Andrew Cooper wrote:
> On 01/09/2025 9:33 am, Jan Beulich wrote:
>> 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.
>
> In Xen, setup_ioapic_ids_from_mpc() has a comment and an xAPIC check at
> the start of the function.
>
> We're lacking Linux commit a38c5380ef9f "x86: io_apic: Split
> setup_ioapic_ids_from_mpc()" which moved the check to the caller.
>
> Perhaps I should s/called/used/ in the commit message?
Maybe, but I wouldn't insist.
Jan
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