[PATCH 09/13] KVM: arm64: Fix WFxT handling of nested virt

Marc Zyngier
2025-09-29T16:05:07Z

The spec for WFxT indicates that the parameter to the WFxT instruction
is relative to the reading of CNTVCT_EL0. This means that the implementation
needs to take the execution context into account, as CNTVOFF_EL2
does not always affect readings of CNTVCT_EL0 (such as when HCR_EL2.E2H
is 1 and that we're in host context).

This also rids us of the last instance of KVM_REG_ARM_TIMER_CNT
outside of the userspace interaction code.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/handle_exit.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index d449e15680e46..415f91ee8bcbf 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -147,7 +147,12 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu)
if (esr & ESR_ELx_WFx_ISS_RV) {
u64 val, now;

- now = kvm_arm_timer_get_reg(vcpu, KVM_REG_ARM_TIMER_CNT);
+ now = kvm_phys_timer_read();
+ if (is_hyp_ctxt(vcpu) && vcpu_el2_e2h_is_set(vcpu))
+ now -= timer_get_offset(vcpu_hvtimer(vcpu));
+ else
+ now -= timer_get_offset(vcpu_vtimer(vcpu));
+
val = vcpu_get_reg(vcpu, kvm_vcpu_sys_get_rt(vcpu));

if (now >= val)
--
2.47.3