KVM: arm64: protected VM: Handle user writes to CNTVCT_EL0/CNTPCT_EL0

Protected VMs doesn't allow setting offsets for virtual and physical
counters, as the offset is always fixed to 0. The VM ioctl is filtered
out based on the cap. However we don't prevent the userspace from trying
to write to the CNTVCT/CNTPCT registers. This would lead to KVM triggering
a WARN() in timer_set_offset() as the vm_offset pointer is set to NULL.

Fix this by always "fixing" the timer offsets to 0 and marking that the
timer offset is set in the kvm->arch.flags at KVM init time for protected
VMs. This prevents the access to the VM specific vm_offset at low cost.
A userspace writing to the CNT*CT_EL0 would observe success, without
any real effect. This is cleaner over spilling "*_is_protected()"
checks and "matches" what we really do in practise. i.e., always run
with "fixed counter offset of 0".

Reported by Sashiko

Link: https://lore.kernel.org/all/20260908164641.416911F00A3A@smtp.kernel.org
Fixes: f7d05ee84a6a ("KVM: arm64: Prevent host from managing timer offsets for protected VMs")
Suggested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Tested-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Link: https://patch.msgid.link/20261007073537.2454351-2-suzuki.poulose@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

0 files changed, 0 insertions, 0 deletions