Xen devel - Aug 2009 - Xen on machines with non-contiguous io-apics

(Mostly a bug report, with a kind of half-fix at the end.)

I have a test box with two IOAPICS which present non-contiguous GSIs
according to the ACPI tables (the first offers 0-24 and the second
32-56).  The latest xen-unstable with current pvops dom0 fails to boot
on this machine, because the dom0 kernel can''t claim any GSIs above
48.  This is because the PHYSDEVOP_alloc_irq_vector implementation
won''t let it get at anything above nr_irqs, which is just the sum of
the number of registers across all APICs.

The patch below fixes this by just setting nr_irqs to the highest GSI
offered by any IOAPIC.  I don''t understand this stuff well enough to
say whether that''s the right fix (and the patch isn''t suitable
for
applying, anyway), but it does make the machine boot.

Steven


diff -r 46b874d60375 xen/arch/x86/io_apic.c
--- a/xen/arch/x86/io_apic.c	Fri Aug 14 12:26:35 2009 +0100
+++ b/xen/arch/x86/io_apic.c	Fri Aug 14 17:18:19 2009 +0100
@@ -2209,6 +2209,8 @@
     }
 }
 
+unsigned highest_gsi(void);
+
 void __init init_ioapic_mappings(void)
 {
     unsigned long ioapic_phys;
@@ -2250,6 +2252,9 @@
             nr_irqs += nr_ioapic_registers[i];
         }
     }
+
+    nr_irqs = highest_gsi();
+
     if ( !smp_found_config || skip_ioapic_setup || nr_irqs < 16 )
         nr_irqs = 16;
     else if ( nr_irqs > PAGE_SIZE * 8 )
diff -r 46b874d60375 xen/arch/x86/mpparse.c
--- a/xen/arch/x86/mpparse.c	Fri Aug 14 12:26:35 2009 +0100
+++ b/xen/arch/x86/mpparse.c	Fri Aug 14 17:18:19 2009 +0100
@@ -945,6 +945,19 @@
 	return;
 }
 
+unsigned highest_gsi(void)
+{
+    unsigned x;
+    unsigned res;
+
+    res = 0;
+    for (x = 0; x < nr_ioapics; x++) {
+        if (res < mp_ioapic_routing[x].gsi_end)
+            res = mp_ioapic_routing[x].gsi_end;
+    }
+    return res;
+}
+
 
 void __init mp_override_legacy_irq (
 	u8			bus_irq,


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>>> Steven Smith <steven.smith@citrix.com> 17.08.09 11:17
>>>
>I have a test box with two IOAPICS which present non-contiguous GSIs
>according to the ACPI tables (the first offers 0-24 and the second
>32-56).  The latest xen-unstable with current pvops dom0 fails to boot
>on this machine, because the dom0 kernel can''t claim any GSIs above
>48.  This is because the PHYSDEVOP_alloc_irq_vector implementation
>won''t let it get at anything above nr_irqs, which is just the sum
of
>the number of registers across all APICs.
>
>The patch below fixes this by just setting nr_irqs to the highest GSI
>offered by any IOAPIC.  I don''t understand this stuff well enough
to
>say whether that''s the right fix (and the patch isn''t
suitable for
>applying, anyway), but it does make the machine boot.
This seems to mostly be in line with upstream Linux, except that it''s
lacking
the fallback for when ACPI is disabled. See acpi_probe_gsi() and its use
in 2.6.31-rcX.

Jan


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