[d/azure][PATCH 1/5] x86/Hyper-V: Set x2apic destination mode to physical when x2apic is available

[Marcelo Henrique Cerri]

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

BugLink: https://bugs.launchpad.net/bugs/1826447

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.

Reviewed-by: Thomas Gleixner <tglx at linutronix.de>
Reviewed-by: Michael Kelley <mikelley at microsoft.com>
Signed-off-by: Lan Tianyu <Tianyu.Lan at microsoft.com>
Signed-off-by: Joerg Roedel <jroedel at suse.de>
(cherry picked from commit 84fdfafab849036b5aefa52824b5cb42e887ef0e)
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 arch/x86/kernel/cpu/mshyperv.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index e81a2db42df7..3fa238a137d2 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -328,6 +328,18 @@ 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.
+	 */
+# ifdef CONFIG_X86_X2APIC
+	if (x2apic_supported())
+		x2apic_phys = 1;
+# endif
+
 #endif
 }
 
-- 
2.20.1