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xen-devel
[Xen-devel] Re: [PATCH RFC] x86/acpi: don't ignore I/O APICs just becaus
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To: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH RFC] x86/acpi: don't ignore I/O APICs just because there's no local APIC |
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From: |
Cyrill Gorcunov <gorcunov@xxxxxxxxx> |
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Date: |
Sat, 13 Jun 2009 00:11:17 +0400 |
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Cc: |
Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx> |
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Tue, 16 Jun 2009 04:21:54 -0700 |
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Mutt/1.5.18 (2008-05-17) |
[Jeremy Fitzhardinge - Fri, Jun 12, 2009 at 11:22:48AM -0700]
> Parse the ACPI MADT for I/O APIC information, even if the cpu has no
> (apparent) local APIC (ie, the CPU's APIC feature flag is clear).
>
> In principle, the local APIC and the I/O APIC are distinct (but related)
> components, which can be independently present.
>
> In practice this can happen in a Xen system, where the hypervisor has
> full control over the local APICs, and delivers interrupts initiated by
> the I/O APICs via Xen's event channel mechanism.
>
> (This eliminates the need for any explicit if (xen...) tests in
> acpi/boot.c)
>
> Signed-off-by: Jeremy Fitzhardinge<jeremy.fitzhardinge@xxxxxxxxxx>
>
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 2410469..19d13e5 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -193,9 +193,6 @@ static int __init acpi_parse_madt(struct
> acpi_table_header *table)
> {
> struct acpi_table_madt *madt = NULL;
>
> - if (!cpu_has_apic)
> - return -EINVAL;
> -
Hi Jeremy,
just for the record -- this removement has a side effect.
Imagine I've passed "disableapic" so I expect as many as
possible apic-related code would not pass thru execution.
Now we would have (say for IBM Summit)
acpi_parse_madt
default_acpi_madt_oem_check
summit_acpi_madt_oem_check
mark_tsc_unstable
setup_summit
Dunno if it harmless or no but it changes kernel behaviour.
cpu_has_apic cleared if disableapic option (which is early
param) passed to kernel.
Just a note. Didn't walk thru all ways.
-- Cyrill
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