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@xxxxxxxxxx>
---
.../selftests/kvm/aarch64/debug-exceptions.c | 21 ++++++++++---------
.../selftests/kvm/include/ucall_common.h | 8 +++++++
2 files changed, 19 insertions(+), 10 deletions(-)
diff --git a/tools/testing/selftests/kvm/aarch64/debug-exceptions.c b/tools/testing/selftests/kvm/aarch64/debug-exceptions.c
index d86c4e4d1c82..c62ec4d7f6a3 100644
--- a/tools/testing/selftests/kvm/aarch64/debug-exceptions.c
+++ b/tools/testing/selftests/kvm/aarch64/debug-exceptions.c
@@ -239,10 +239,6 @@ static void guest_svc_handler(struct ex_regs *regs)
svc_addr = regs->pc;
}
-enum single_step_op {
- SINGLE_STEP_ENABLE = 0,
-};
-
static void guest_code_ss(int test_cnt)
{
uint64_t i;
@@ -253,8 +249,16 @@ static void guest_code_ss(int test_cnt)
w_bvr = i << 2;
w_wvr = i << 2;
- /* Enable Single Step execution */
- GUEST_SYNC(SINGLE_STEP_ENABLE);
+ /*
+ * Enable Single Step execution. Note! This _must_ be a bare
+ * ucall as the ucall() path uses atomic operations to manage
+ * the ucall structures, and the built-in "atomics" are usually
+ * implemented via exclusive access instructions. The exlusive
+ * monitor is cleared on ERET, and so taking debug exceptions
+ * during a LDREX=>STREX sequence will prevent forward progress
+ * and hang the guest/test.
+ */
+ GUEST_UCALL_NONE();
/*
* The userspace will verify that the pc is as expected during
@@ -356,12 +360,9 @@ void test_single_step_from_userspace(int test_cnt)
break;
}
- TEST_ASSERT(cmd == UCALL_SYNC,
+ TEST_ASSERT(cmd == UCALL_NONE,
"Unexpected ucall cmd 0x%lx", cmd);
- TEST_ASSERT(uc.args[1] == SINGLE_STEP_ENABLE,
- "Unexpected ucall action 0x%lx", uc.args[1]);
-
debug.control = KVM_GUESTDBG_ENABLE |
KVM_GUESTDBG_SINGLESTEP;
ss_enable = true;
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)
--
2.38.1.584.g0f3c55d4c2-goog
