Re: [patch 2/4] x86, vtd: fix the vt-d fault handling irqmigration in the x2apic mode

[Bjorn Helgaas]

On Tue, Nov 30, 2010 at 10:22:27PM -0800, Suresh Siddha wrote:
> From: Kenji Kaneshige <kaneshige.kenji@xxxxxxxxxxxxxx>
> Subject: x86, vtd: fix the vt-d fault handling irq migration in the x2apic mode
> 
> In x2apic mode, we need to set the upper address register of the fault
> handling interrupt register of the vt-d hardware. Without this
> irq migration of the vt-d fault handling interrupt is broken.
> 
> Signed-off-by: Kenji Kaneshige <kaneshige.kenji@xxxxxxxxxxxxxx>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
> Cc: stable@xxxxxxxxxx [v2.6.32+]
> ---
>  arch/x86/kernel/apic/io_apic.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> Index: tip/arch/x86/kernel/apic/io_apic.c
> ===================================================================
> --- tip.orig/arch/x86/kernel/apic/io_apic.c
> +++ tip/arch/x86/kernel/apic/io_apic.c
> @@ -3367,6 +3367,8 @@ dmar_msi_set_affinity(struct irq_data *d
>  	msg.data |= MSI_DATA_VECTOR(cfg->vector);
>  	msg.address_lo &= ~MSI_ADDR_DEST_ID_MASK;
>  	msg.address_lo |= MSI_ADDR_DEST_ID(dest);
> +	if (x2apic_mode)
> +		msg.address_hi = MSI_ADDR_BASE_HI | MSI_ADDR_EXT_DEST_ID(dest);

Is it necessary to test x2apic_mode here?  It looks like
MSI_ADDR_EXT_DEST_ID() gives you everything above the low 8
bits of the APIC ID.  If those bits are always zero except in
x2apic_mode, we might not need the test.

Does the ia64 dmar_msi_set_affinity() need the same fix?

Why do we have both x2apic_enabled() and x2apic_mode?  They
seem sort of redundant.  (Not related to this patch, of course.)

Bjorn
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