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KVM: arm64: Prevent host from managing timer offsets for protected VMs

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For protected VMs, the guest's timer offset state should not be
controlled by the host and must always run with a virtual counter offset
of 0. The existing timer logic allowed the host to set and manage the
timer counter offsets for protected VMs in certain cases.

Disable all host-side management of timer offsets for protected VMs by
adding checks in the relevant code paths.

Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20251211104710.151771-10-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Fuad Tabba 2025-12-11 10:47:09 +00:00 committed by Marc Zyngier
parent b12b3b04f6
commit f7d05ee84a
1 changed files with 13 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
arch/arm64/kvm/arch_timer.c
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@ -1056,10 +1056,14 @@ static void timer_context_init(struct kvm_vcpu *vcpu, int timerid)
ctxt->timer_id = timerid;
if (timerid == TIMER_VTIMER)
ctxt->offset.vm_offset = &kvm->arch.timer_data.voffset;
else
ctxt->offset.vm_offset = &kvm->arch.timer_data.poffset;
if (!kvm_vm_is_protected(vcpu->kvm)) {
if (timerid == TIMER_VTIMER)
ctxt->offset.vm_offset = &kvm->arch.timer_data.voffset;
else
ctxt->offset.vm_offset = &kvm->arch.timer_data.poffset;
} else {
ctxt->offset.vm_offset = NULL;
}
hrtimer_setup(&ctxt->hrtimer, kvm_hrtimer_expire, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
@ -1083,7 +1087,8 @@ void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
timer_context_init(vcpu, i);
/* Synchronize offsets across timers of a VM if not already provided */
if (!test_bit(KVM_ARCH_FLAG_VM_COUNTER_OFFSET, &vcpu->kvm->arch.flags)) {
if (!vcpu_is_protected(vcpu) &&
!test_bit(KVM_ARCH_FLAG_VM_COUNTER_OFFSET, &vcpu->kvm->arch.flags)) {
timer_set_offset(vcpu_vtimer(vcpu), kvm_phys_timer_read());
timer_set_offset(vcpu_ptimer(vcpu), 0);
}
@ -1687,6 +1692,9 @@ int kvm_vm_ioctl_set_counter_offset(struct kvm *kvm,
if (offset->reserved)
return -EINVAL;
if (kvm_vm_is_protected(kvm))
return -EINVAL;
mutex_lock(&kvm->lock);
if (!kvm_trylock_all_vcpus(kvm)) {