[PATCH kvmtool 5/5] arm64: Query counter-offset support on the VM fd

[Fuad Tabba <fuad.tabba@linux.dev>]

kvm__arch_set_counter_offset() probes KVM_CAP_COUNTER_OFFSET with
kvm__supports_extension(), which issues KVM_CHECK_EXTENSION on the
global /dev/kvm fd. That reports the host's raw capabilities, unaware of
any per-VM restrictions.

pKVM does not offer the counter offset to a protected VM, and reflects
that on the VM fd alone. kvmtool's own check passes, and the
KVM_ARM_SET_COUNTER_OFFSET that follows is refused by
commit b12b3b04f6ba ("KVM: arm64: Check whether a VM IOCTL is allowed
in pKVM"):

  KVM_ARM_SET_COUNTER_OFFSET: Invalid argument

Query it on the VM fd via kvm__supports_vm_extension(), so
--counter-offset on a protected VM fails with kvmtool's own message:

  Fatal: No support for global counter offset

Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arm64/kvm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arm64/kvm.c b/arm64/kvm.c
index 36b3284..0bb3535 100644
--- a/arm64/kvm.c
+++ b/arm64/kvm.c
@@ -155,7 +155,7 @@ static void kvm__arch_set_counter_offset(struct kvm *kvm)
 	if (!kvm->cfg.arch.counter_offset)
 		return;
 
-	if (!kvm__supports_extension(kvm, KVM_CAP_COUNTER_OFFSET))
+	if (!kvm__supports_vm_extension(kvm, KVM_CAP_COUNTER_OFFSET))
 		die("No support for global counter offset");
 
 	if (ioctl(kvm->vm_fd, KVM_ARM_SET_COUNTER_OFFSET, &offset))
-- 
2.39.5