[PATCH V2 1/3] x86/Hyper-V: Set x2apic destination mode to physical when x2apic is available

[lantianyu1986 at gmail.com]

From: Lan Tianyu <Tianyu.Lan at microsoft.com>

Hyper-V doesn't provide irq remapping for IO-APIC. To enable x2apic,
set x2apic destination mode to physcial mode when x2apic is available
and Hyper-V IOMMU driver makes sure cpus assigned with IO-APIC irqs have
8-bit APIC id.

Signed-off-by: Lan Tianyu <Tianyu.Lan at microsoft.com>
---
Change since v1:
       - Remove redundant extern for x2apic_phys
---
 arch/x86/kernel/cpu/mshyperv.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index e81a2db..4bd6d90 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -328,6 +328,16 @@ static void __init ms_hyperv_init_platform(void)
 # ifdef CONFIG_SMP
 	smp_ops.smp_prepare_boot_cpu = hv_smp_prepare_boot_cpu;
 # endif
+
+/*
+ * Hyper-V doesn't provide irq remapping for IO-APIC. To enable x2apic,
+ * set x2apic destination mode to physcial mode when x2apic is available
+ * and Hyper-V IOMMU driver makes sure cpus assigned with IO-APIC irqs
+ * have 8-bit APIC id.
+ */
+	if (IS_ENABLED(CONFIG_HYPERV_IOMMU) && x2apic_supported())
+		x2apic_phys = 1;
+
 #endif
 }
 
-- 
2.7.4