[SRU][bionic/azure-4.15][PATCH 3/5] x86/Hyper-V: Set x2apic destination mode to physical when x2apic is available

[Bartlomiej Zolnierkiewicz]

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

BugLink: https://bugs.launchpad.net/bugs/1951924

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>
(backported from 84fdfafab849036b5aefa52824b5cb42e887ef0e)
Signed-off-by: Bartlomiej Zolnierkiewicz <bartlomiej.zolnierkiewicz 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 89d86ff64b6f..d603867bf251 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -324,6 +324,18 @@ static void __init ms_hyperv_init_platform(void)
 	if (ms_hyperv.misc_features & HV_X64_STIMER_DIRECT_MODE_AVAILABLE)
 		alloc_intr_gate(HYPERV_STIMER0_VECTOR,
 				hv_stimer0_callback_vector);
+
+	/*
+	 * 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
 }
 
-- 
2.25.1