[tip: x86/urgent] x86/acrn: Allow ACRN guest to use X2APIC mode

[tip-bot2 for Shuo Liu]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     86d709ce30eaa65706090865662a08d7bdd30c54
Gitweb:        https://git.kernel.org/tip/86d709ce30eaa65706090865662a08d7bdd30c54
Author:        Shuo Liu <shuo.a.liu@xxxxxxxxx>
AuthorDate:    Thu, 06 Aug 2020 19:38:02 +08:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 07 Aug 2020 01:32:00 +02:00

x86/acrn: Allow ACRN guest to use X2APIC mode

The ACRN Hypervisor did not support x2APIC and thus x2APIC support was
disabled by always returning false when VM checked for x2APIC support.

ACRN received full support of x2APIC and exports the capability through
CPUID feature bits.

Let VM decide if it needs to switch to x2APIC mode according to CPUID
features.

Originally-by: Yakui Zhao <yakui.zhao@xxxxxxxxx>
Signed-off-by: Shuo Liu <shuo.a.liu@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Link: https://lore.kernel.org/r/20200806113802.9325-1-shuo.a.liu@xxxxxxxxx
---
 arch/x86/kernel/cpu/acrn.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/acrn.c b/arch/x86/kernel/cpu/acrn.c
index 1da9b1c..3b08cdf 100644
--- a/arch/x86/kernel/cpu/acrn.c
+++ b/arch/x86/kernel/cpu/acrn.c
@@ -11,6 +11,7 @@
 
 #include <linux/interrupt.h>
 #include <asm/apic.h>
+#include <asm/cpufeatures.h>
 #include <asm/desc.h>
 #include <asm/hypervisor.h>
 #include <asm/idtentry.h>
@@ -29,12 +30,7 @@ static void __init acrn_init_platform(void)
 
 static bool acrn_x2apic_available(void)
 {
-	/*
-	 * x2apic is not supported for now. Future enablement will have to check
-	 * X86_FEATURE_X2APIC to determine whether x2apic is supported in the
-	 * guest.
-	 */
-	return false;
+	return boot_cpu_has(X86_FEATURE_X2APIC);
 }
 
 static void (*acrn_intr_handler)(void);