KVM: selftests: fix max_guest_memory_test with more that 256 vCPUs

max_guest_memory_test uses ucalls to sync with the host, but
it also resets the guest RIP back to its initial value in between
tests stages.

This makes the guest never reach the code which frees the ucall struct
and since a fixed pool of 512 ucall structs is used, the test starts
to fail when more that 256 vCPUs are used.

Fix that by replacing the manual register reset with a loop in
the guest code.

Signed-off-by: Maxim Levitsky <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

Author: Maxim Levitsky

tools/testing/selftests/kvm/max_guest_memory_test.c

@@ -22,10 +22,11 @@ static void guest_code(uint64_t start_gpa, uint64_t end_gpa, uint64_t stride)
 {
 	uint64_t gpa;
 
-	for (gpa = start_gpa; gpa < end_gpa; gpa += stride)
-		*((volatile uint64_t *)gpa) = gpa;
-
-	GUEST_DONE();
+	for (;;) {
+		for (gpa = start_gpa; gpa < end_gpa; gpa += stride)
+			*((volatile uint64_t *)gpa) = gpa;
+		GUEST_SYNC(0);
+	}
 }
 
 struct vcpu_info {
@@ -55,7 +56,7 @@ static void rendezvous_with_boss(void)
 static void run_vcpu(struct kvm_vcpu *vcpu)
 {
 	vcpu_run(vcpu);
-	TEST_ASSERT_EQ(get_ucall(vcpu, NULL), UCALL_DONE);
+	TEST_ASSERT_EQ(get_ucall(vcpu, NULL), UCALL_SYNC);
 }
 
 static void *vcpu_worker(void *data)
@@ -64,17 +65,13 @@ static void *vcpu_worker(void *data)
 	struct kvm_vcpu *vcpu = info->vcpu;
 	struct kvm_vm *vm = vcpu->vm;
 	struct kvm_sregs sregs;
-	struct kvm_regs regs;
 
 	vcpu_args_set(vcpu, 3, info->start_gpa, info->end_gpa, vm->page_size);
 
-	/* Snapshot regs before the first run. */
-	vcpu_regs_get(vcpu, &regs);
 	rendezvous_with_boss();
 
 	run_vcpu(vcpu);
 	rendezvous_with_boss();
-	vcpu_regs_set(vcpu, &regs);
 	vcpu_sregs_get(vcpu, &sregs);
 #ifdef __x86_64__
 	/* Toggle CR0.WP to trigger a MMU context reset. */