[PATCH v2 2/2] KVM: arm64: timers: Save restore CVAL of a ptimer across guest entry and exits

[Ganapatrao Kulkarni]

As per FEAT_ECV, when HCR_EL2.{E2H, TGE} == {1, 1}, Enhanced Counter
Virtualization functionality is disabled and CNTPOFF_EL2 value is treated
as zero. On VHE host, E2H and TGE are set, hence it is required
to save Guest's CVAL to memory and increment it by CNTPOFF_EL2 at
guest exit to avoid false physical timer interrupts and also
restore back the CVAL with saved value before the guest entry.

Signed-off-by: Ganapatrao Kulkarni <gankulkarni at os.amperecomputing.com>
---
 arch/arm64/kvm/arch_timer.c     | 60 ++++++++++++++++++++++++++++++---
 arch/arm64/kvm/hyp/vhe/switch.c | 13 +++++++
 include/kvm/arm_arch_timer.h    |  1 +
 3 files changed, 69 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index 98b0e8ac02ae..9fe3fa6ed98a 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -514,6 +514,59 @@ static void set_cntpoff(u64 cntpoff)
 		write_sysreg_s(cntpoff, SYS_CNTPOFF_EL2);
 }
 
+static void ptimer_cval_save(struct arch_timer_context *ctx, u64 offset)
+{
+	unsigned long flags;
+	u64 cval;
+
+	local_irq_save(flags);
+	cval = read_sysreg_el0(SYS_CNTP_CVAL);
+	timer_set_cval(ctx, cval);
+	cval += offset;
+	write_sysreg_el0(cval, SYS_CNTP_CVAL);
+	isb();
+	local_irq_restore(flags);
+}
+
+static void ptimer_cval_restore(struct arch_timer_context *ctx, u64 offset)
+{
+	unsigned long flags;
+	u64 cval;
+
+	local_irq_save(flags);
+	cval = timer_get_cval(ctx);
+	write_sysreg_el0(cval, SYS_CNTP_CVAL);
+	isb();
+	local_irq_restore(flags);
+}
+
+void kvm_ptimer_cval_save_restore(struct kvm_vcpu *vcpu, bool save)
+{
+	struct timer_map map;
+	struct arch_timer_cpu *timer;
+	struct arch_timer_context *ctxp;
+	u64 offset;
+
+	get_timer_map(vcpu, &map);
+	ctxp = map.direct_ptimer;
+
+	if (unlikely(ctxp == NULL))
+		return;
+
+	offset = timer_get_offset(ctxp);
+	if (!offset)
+		return;
+
+	timer = vcpu_timer(ctxp->vcpu);
+	if (!timer->enabled || !ctxp->loaded)
+		return;
+
+	if (save)
+		ptimer_cval_save(ctxp, offset);
+	else
+		ptimer_cval_restore(ctxp, offset);
+}
+
 static void timer_save_state(struct arch_timer_context *ctx)
 {
 	struct arch_timer_cpu *timer = vcpu_timer(ctx->vcpu);
@@ -562,9 +615,7 @@ static void timer_save_state(struct arch_timer_context *ctx)
 		timer_set_ctl(ctx, read_sysreg_el0(SYS_CNTP_CTL));
 		cval = read_sysreg_el0(SYS_CNTP_CVAL);
 
-		if (!has_cntpoff())
-			cval -= timer_get_offset(ctx);
-
+		cval -= timer_get_offset(ctx);
 		timer_set_cval(ctx, cval);
 
 		/* Disable the timer */
@@ -650,8 +701,7 @@ static void timer_restore_state(struct arch_timer_context *ctx)
 		cval = timer_get_cval(ctx);
 		offset = timer_get_offset(ctx);
 		set_cntpoff(offset);
-		if (!has_cntpoff())
-			cval += offset;
+		cval += offset;
 		write_sysreg_el0(cval, SYS_CNTP_CVAL);
 		isb();
 		write_sysreg_el0(timer_get_ctl(ctx), SYS_CNTP_CTL);
diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index 561cb53e19ce..097fcaf7b208 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -100,6 +100,10 @@ static void __activate_traps(struct kvm_vcpu *vcpu)
 		hcr |= vhcr_el2;
 	}
 
+	/* Restore CVAL */
+	if (has_cntpoff())
+		kvm_ptimer_cval_save_restore(vcpu, false);
+
 	___activate_traps(vcpu, hcr);
 
 	val = read_sysreg(cpacr_el1);
@@ -141,6 +145,15 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
 
 	___deactivate_traps(vcpu);
 
+	/*
+	 * For VHE Host, HCR_EL2.{E2H, TGE} is {1, 1}, FEAT_ECV
+	 * is disabled and CNTPOFF_EL2 value is treated as zero.
+	 * Hence, need to save guest written CVAL in memory and
+	 * increment PTIMER's CVAL by CNTPOFF to avoid false interrupt.
+	 */
+	if (has_cntpoff())
+		kvm_ptimer_cval_save_restore(vcpu, true);
+
 	write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
 
 	/*
diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
index ea77a569a907..ce3f4d9e7dd4 100644
--- a/include/kvm/arm_arch_timer.h
+++ b/include/kvm/arm_arch_timer.h
@@ -117,6 +117,7 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu);
 void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu);
 
 void kvm_timer_init_vhe(void);
+void kvm_ptimer_cval_save_restore(struct kvm_vcpu *vcpu, bool save);
 
 #define vcpu_timer(v)	(&(v)->arch.timer_cpu)
 #define vcpu_get_timer(v,t)	(&vcpu_timer(v)->timers[(t)])
-- 
2.41.0