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[RFC,5/6] arm64: hyperv: Enable userspace to read cntvct

Message ID 20191216001922.23008-6-boqun.feng@gmail.com (mailing list archive)
State New, archived
Headers show
Series vDSO support for Hyper-V guest on ARM64 | expand

Commit Message

Boqun Feng Dec. 16, 2019, 12:19 a.m. UTC 
Since reading hyperv-timer clocksource requires reading cntvct,
userspace should be allowed to read it, otherwise reading cntvct will
result in traps, which makes vsyscall's cost similar compared to
syscall's.

So enable it on every cpu when a Hyper-V guest booting up.

Signed-off-by: Boqun Feng (Microsoft) <boqun.feng@gmail.com>
---
 arch/arm64/hyperv/hv_init.c | 7 +++++++
 1 file changed, 7 insertions(+)
diff mbox series

Patch

diff --git a/arch/arm64/hyperv/hv_init.c b/arch/arm64/hyperv/hv_init.c
index 86e4621d5885..1ea97ecfb143 100644
--- a/arch/arm64/hyperv/hv_init.c
+++ b/arch/arm64/hyperv/hv_init.c
@@ -27,6 +27,7 @@ 
 #include <linux/sched_clock.h>
 #include <asm-generic/bug.h>
 #include <asm/hyperv-tlfs.h>
+#include <asm/arch_timer.h>
 #include <asm/mshyperv.h>
 #include <asm/sysreg.h>
 #include <clocksource/hyperv_timer.h>
@@ -45,6 +46,7 @@  EXPORT_SYMBOL_GPL(hv_max_vp_index);
 static int hv_cpu_init(unsigned int cpu)
 {
 	u64 msr_vp_index;
+	u32 cntkctl;
 
 	hv_get_vp_index(msr_vp_index);
 
@@ -53,6 +55,11 @@  static int hv_cpu_init(unsigned int cpu)
 	if (msr_vp_index > hv_max_vp_index)
 		hv_max_vp_index = msr_vp_index;
 
+	/* Enable EL0 to access cntvct */
+	cntkctl = arch_timer_get_cntkctl();
+	cntkctl |= ARCH_TIMER_USR_VCT_ACCESS_EN;
+	arch_timer_set_cntkctl(cntkctl);
+
 	return 0;
 }