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Diffstat (limited to 'tools/testing/selftests/kvm/x86_64/sync_regs_test.c')
-rw-r--r--tools/testing/selftests/kvm/x86_64/sync_regs_test.c21
1 files changed, 11 insertions, 10 deletions
diff --git a/tools/testing/selftests/kvm/x86_64/sync_regs_test.c b/tools/testing/selftests/kvm/x86_64/sync_regs_test.c
index 11c2a70a7b87..5c8224256294 100644
--- a/tools/testing/selftests/kvm/x86_64/sync_regs_test.c
+++ b/tools/testing/selftests/kvm/x86_64/sync_regs_test.c
@@ -22,18 +22,19 @@
#define VCPU_ID 5
+#define UCALL_PIO_PORT ((uint16_t)0x1000)
+
+/*
+ * ucall is embedded here to protect against compiler reshuffling registers
+ * before calling a function. In this test we only need to get KVM_EXIT_IO
+ * vmexit and preserve RBX, no additional information is needed.
+ */
void guest_code(void)
{
- /*
- * use a callee-save register, otherwise the compiler
- * saves it around the call to GUEST_SYNC.
- */
- register u32 stage asm("rbx");
- for (;;) {
- GUEST_SYNC(0);
- stage++;
- asm volatile ("" : : "r" (stage));
- }
+ asm volatile("1: in %[port], %%al\n"
+ "add $0x1, %%rbx\n"
+ "jmp 1b"
+ : : [port] "d" (UCALL_PIO_PORT) : "rax", "rbx");
}
static void compare_regs(struct kvm_regs *left, struct kvm_regs *right)