Recently the generic timer test of kvm-unit-tests failed to complete
(stalled) when a physical timer is being used. This issue is caused
by incorrect update of CNT_CVAL when TimerValue is being accessed,
introduced by 'Commit 84135d3d18da ("KVM: arm/arm64: consolidate arch
timer trap handlers")'. According to Arm ARM, the read/write behavior
of accesses to TimeValue registers is expected to be:
* READ: TimerValue = (CompareValue – (Counter - Offset)
* WRITE: CompareValue = ((Counter - Offset) + Sign(TimerValue)
This patch fixes the TVAL read/write code path according to the
specification.
Signed-off-by: Wei Huang <wei@xxxxxxxxxx>
---
virt/kvm/arm/arch_timer.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index 3417f2dbc366..d43308dc3617 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -812,7 +812,7 @@ static u64 kvm_arm_timer_read(struct kvm_vcpu *vcpu,
switch (treg) {
case TIMER_REG_TVAL:
- val = kvm_phys_timer_read() - timer->cntvoff - timer->cnt_cval;
+ val = timer->cnt_cval - kvm_phys_timer_read() + timer->cntvoff;
break;
case TIMER_REG_CTL:
@@ -858,7 +858,7 @@ static void kvm_arm_timer_write(struct kvm_vcpu *vcpu,
{
switch (treg) {
case TIMER_REG_TVAL:
- timer->cnt_cval = val - kvm_phys_timer_read() - timer->cntvoff;
+ timer->cnt_cval = kvm_phys_timer_read() - timer->cntvoff + val;
break;
case TIMER_REG_CTL:
--
2.14.5
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