[PATCH v2 2/3] KVM: arm64: Fix timer offsets for non-protected VMs

[Mostafa Saleh]

With pKVM, protected VMs always have offset of zero.
However, timer offsets for non-protected guests fail to take effect
for two reasons:
1) In __timer_enable_traps(), enabling of traps check for
   is_protected_kvm_enabled() rather than vcpu_is_protected(vcpu)

2) The vcpu timer offsets were never initialised and kept as NULL.

This is problematic for cases when the timer is trapped in the
hypervisor as the with the case of broken CNTVOFF_EL2, which leads
to the hypervisor and host using different offsets and causing VM
hangs.

This can be confirmed by running the arch_timer selftest which fails:
./arch_timer -o 100000000
Random seed: 0x6b8b4567
Guest assert failed,  vcpu 0; stage; 3; iter: 0
==== Test Assertion Failure ====
  arm64/arch_timer.c:137: config_iter + 1 == irq_iter
  pid=310 tid=312 errno=4 - Interrupted system call
Guest assert failed,  vcpu 3; stage; 3; iter: 0
Guest assert failed,  vcpu 1; stage; 3; iter: 0
==== Test Assertion Failure ====
  arm64/arch_timer.c:137: config_iter + 1 == irq_iter
  pid=310 tid=313 errno=4 - Interrupted system call
Guest assert failed,  vcpu 2; stage; 3; iter: 0
==== Test Assertion Failure ====
  arm64/arch_timer.c:137: config_iter + 1 == irq_iter
  pid=310 tid=314 errno=4 - Interrupted system call
[...]

After the fix:

./arch_timer -o 100000000
Random seed: 0x6b8b4567
PASS(vCPU-1).
PASS(vCPU-3).
PASS(vCPU-0).
PASS(vCPU-2)

Reported-by: Sashiko <sashiko-bot at kernel.org>
Fixes: cb0c272acebd ("KVM: arm64: Initialize the hypervisor's VM state at EL2")
Signed-off-by: Mostafa Saleh <smostafa at google.com>
---
 arch/arm64/kvm/hyp/nvhe/pkvm.c     | 14 ++++++++++++++
 arch/arm64/kvm/hyp/nvhe/timer-sr.c |  6 +++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 24d6f164129a..89f3d5fb55ca 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -529,6 +529,20 @@ static int init_pkvm_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu,
 	hyp_vcpu->vcpu.arch.cflags = READ_ONCE(host_vcpu->arch.cflags);
 	hyp_vcpu->vcpu.arch.mp_state.mp_state = KVM_MP_STATE_STOPPED;
 
+	if (!pkvm_hyp_vcpu_is_protected(hyp_vcpu)) {
+		/*
+		 * Timer offsets are pointing to the untrusted KVM copy,
+		 * which is pinned in __pkvm_init_vm() for the VM life time.
+		 * It is worth noting that hyp_vm->host_kvm points to an EL2
+		 * linear map address and timer_get_offset() will use
+		 * kern_hyp_va() which is safe as it is idempotent.
+		 */
+		vcpu_vtimer(&hyp_vcpu->vcpu)->offset.vm_offset =
+			&hyp_vm->host_kvm->arch.timer_data.voffset;
+		vcpu_ptimer(&hyp_vcpu->vcpu)->offset.vm_offset =
+			&hyp_vm->host_kvm->arch.timer_data.poffset;
+	}
+
 	ret = pkvm_vcpu_init_sysregs(hyp_vcpu);
 	if (ret)
 		goto done;
diff --git a/arch/arm64/kvm/hyp/nvhe/timer-sr.c b/arch/arm64/kvm/hyp/nvhe/timer-sr.c
index ff176f4ce7de..51b4f5010b66 100644
--- a/arch/arm64/kvm/hyp/nvhe/timer-sr.c
+++ b/arch/arm64/kvm/hyp/nvhe/timer-sr.c
@@ -45,11 +45,11 @@ void __timer_enable_traps(struct kvm_vcpu *vcpu)
 	/*
 	 * Disallow physical timer access for the guest
 	 * Physical counter access is allowed if no offset is enforced
-	 * or running protected (we don't offset anything in this case).
+	 * or running a protected VM (we don't offset anything in this case).
 	 */
 	clr = CNTHCTL_EL1PCEN;
-	if (is_protected_kvm_enabled() ||
-	    !kern_hyp_va(vcpu->kvm)->arch.timer_data.poffset)
+	if (vcpu_is_protected(vcpu) ||
+	    !timer_get_offset(vcpu_ptimer(vcpu)))
 		set |= CNTHCTL_EL1PCTEN;
 	else
 		clr |= CNTHCTL_EL1PCTEN;
-- 
2.55.0.654.g21b8a5bc05-goog