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xen-devel
[Xen-devel] Re: [PATCH] Fix when booting Xen+Linux under QEMU.
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To: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH] Fix when booting Xen+Linux under QEMU. |
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From: |
Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> |
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Date: |
Fri, 10 Dec 2010 13:02:52 +0000 |
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Cc: |
"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Stefano, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, Rzeszutek Wilk <konrad@xxxxxxxxxx>, Konrad |
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Fri, 10 Dec 2010 05:03:54 -0800 |
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Alpine 2.00 (DEB 1167 2008-08-23) |
On Thu, 9 Dec 2010, Jeremy Fitzhardinge wrote:
> 2. kill the ioapic dummy page hack (I'm assuming that would be
> trivial - at least to make it all zero - because the kernel won't
> care about the number of GSIs at that point)
That wouldn't work: mp_register_ioapic reads the number of entries for
each ioapic and it cannot be zero, because later on mp_find_ioapic is
going to find the ioapic a particular gsi belongs to based on the
previous results.
Mp_register_ioapic also increases gsi_top that ends up influencing the
value of nr_irqs_gsi.
Considering that nr_irqs is not a real upper limit on Xen because you
usually have at least 1024 evtchns anyway, I think we should reimplement
arch_probe_nr_irqs on Xen to set nr_irqs appropriately.
Something like this:
#define NR_EVTCHNS (sizeof(unsigned long) * 8 * sizeof(unsigned long))
int __init arch_probe_nr_irqs(void)
{
if (xen_domain())
nr_irqs = NR_EVTCHNS;
return NR_IRQS_LEGACY;
}
The problem is that #ifdef CONFIG_SPARSE_IRQ io_apic.c reimplements
arch_probe_nr_irqs too but only if CONFIG_PCI_MSI is also defined
nr_irqs is set high enough by that function.
So to work around this problem we might have to redefine
arch_probe_nr_irqs only #if !defined(CONFIG_SPARSE_IRQ) and we might also
have to automatically enable CONFIG_PCI_MSI if the user selects
CONFIG_SPARSE_IRQ on XEN somehow.
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