KVM: arm64: selftests: Enable single-step without a "full" ucall()

Add a new ucall hook, GUEST_UCALL_NONE(), to allow tests to make ucalls
without allocating a ucall struct, and use it to enable single-step
in ARM's debug-exceptions test.  Like the disable single-step path, the
enabling path also needs to ensure that no exclusive access sequences are
attempted after enabling single-step, as the exclusive monitor is cleared
on ERET from the debug exception taken to EL2.

The test currently "works" because clear_bit() isn't actually an atomic
operation... yet.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221119013450.2643007-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/tools/testing/selftests/kvm/include/ucall_common.h b/tools/testing/selftests/kvm/include/ucall_common.h
index bdd373189a77..1a6aaef5ccae 100644
--- a/tools/testing/selftests/kvm/include/ucall_common.h
+++ b/tools/testing/selftests/kvm/include/ucall_common.h
@@ -35,6 +35,14 @@ void ucall(uint64_t cmd, int nargs, ...);
 uint64_t get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc);
 void ucall_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa);
 
+/*
+ * Perform userspace call without any associated data.  This bare call avoids
+ * allocating a ucall struct, which can be useful if the atomic operations in
+ * the full ucall() are problematic and/or unwanted.  Note, this will come out
+ * as UCALL_NONE on the backend.
+ */
+#define GUEST_UCALL_NONE()	ucall_arch_do_ucall((vm_vaddr_t)NULL)
+
 #define GUEST_SYNC_ARGS(stage, arg1, arg2, arg3, arg4)	\
 				ucall(UCALL_SYNC, 6, "hello", stage, arg1, arg2, arg3, arg4)
 #define GUEST_SYNC(stage)	ucall(UCALL_SYNC, 2, "hello", stage)