Commit ac17892e authored by Yosry Ahmed's avatar Yosry Ahmed Committed by Sean Christopherson
Browse files

KVM: selftests: Add a test for LBR save/restore (ft. nested) 



Add a selftest exercising save/restore with usage of LBRs in both L1 and
L2, and making sure all LBRs remain intact.

Signed-off-by: default avatarYosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260303003421.2185681-5-yosry@kernel.org


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 3700f078

tools/testing/selftests/kvm/Makefile.kvm

+1 −0
Original line number Diff line number Diff line
@@ -112,6 +112,7 @@ TEST_GEN_PROGS_x86 += x86/svm_vmcall_test 
TEST_GEN_PROGS_x86 += x86/svm_int_ctl_test

TEST_GEN_PROGS_x86 += x86/svm_nested_shutdown_test

TEST_GEN_PROGS_x86 += x86/svm_nested_soft_inject_test

TEST_GEN_PROGS_x86 += x86/svm_lbr_nested_state

TEST_GEN_PROGS_x86 += x86/tsc_scaling_sync

TEST_GEN_PROGS_x86 += x86/sync_regs_test

TEST_GEN_PROGS_x86 += x86/ucna_injection_test

tools/testing/selftests/kvm/include/x86/processor.h

+5 −0
Original line number Diff line number Diff line
@@ -1360,6 +1360,11 @@ static inline bool kvm_is_ignore_msrs(void) 
	return get_kvm_param_bool("ignore_msrs");

}



static inline bool kvm_is_lbrv_enabled(void)

{

	return !!get_kvm_amd_param_integer("lbrv");

}



uint64_t *vm_get_pte(struct kvm_vm *vm, uint64_t vaddr);



uint64_t kvm_hypercall(uint64_t nr, uint64_t a0, uint64_t a1, uint64_t a2,

tools/testing/selftests/kvm/x86/svm_lbr_nested_state.c

0 → 100644
+145 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0-only

/*

 * Copyright (C) 2026, Google, Inc.

 */



#include "test_util.h"

#include "kvm_util.h"

#include "processor.h"

#include "svm_util.h"





#define L2_GUEST_STACK_SIZE 64



#define DO_BRANCH() do { asm volatile("jmp 1f\n 1: nop"); } while (0)



struct lbr_branch {

	u64 from, to;

};



volatile struct lbr_branch l2_branch;



#define RECORD_AND_CHECK_BRANCH(b)					\

do {									\

	wrmsr(MSR_IA32_DEBUGCTLMSR, DEBUGCTLMSR_LBR);			\

	DO_BRANCH();							\

	(b)->from = rdmsr(MSR_IA32_LASTBRANCHFROMIP);			\

	(b)->to = rdmsr(MSR_IA32_LASTBRANCHTOIP);			\

	/* Disable LBR right after to avoid overriding the IPs */	\

	wrmsr(MSR_IA32_DEBUGCTLMSR, 0);					\

									\

	GUEST_ASSERT_NE((b)->from, 0);					\

	GUEST_ASSERT_NE((b)->to, 0);					\

} while (0)



#define CHECK_BRANCH_MSRS(b)						\

do {									\

	GUEST_ASSERT_EQ((b)->from, rdmsr(MSR_IA32_LASTBRANCHFROMIP));	\

	GUEST_ASSERT_EQ((b)->to, rdmsr(MSR_IA32_LASTBRANCHTOIP));	\

} while (0)



#define CHECK_BRANCH_VMCB(b, vmcb)					\

do {									\

	GUEST_ASSERT_EQ((b)->from, vmcb->save.br_from);			\

	GUEST_ASSERT_EQ((b)->to, vmcb->save.br_to);			\

} while (0)



static void l2_guest_code(struct svm_test_data *svm)

{

	/* Record a branch, trigger save/restore, and make sure LBRs are intact */

	RECORD_AND_CHECK_BRANCH(&l2_branch);

	GUEST_SYNC(true);

	CHECK_BRANCH_MSRS(&l2_branch);

	vmmcall();

}



static void l1_guest_code(struct svm_test_data *svm, bool nested_lbrv)

{

	unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];

	struct vmcb *vmcb = svm->vmcb;

	struct lbr_branch l1_branch;



	/* Record a branch, trigger save/restore, and make sure LBRs are intact */

	RECORD_AND_CHECK_BRANCH(&l1_branch);

	GUEST_SYNC(true);

	CHECK_BRANCH_MSRS(&l1_branch);



	/* Run L2, which will also do the same */

	generic_svm_setup(svm, l2_guest_code,

			  &l2_guest_stack[L2_GUEST_STACK_SIZE]);



	if (nested_lbrv)

		vmcb->control.virt_ext = LBR_CTL_ENABLE_MASK;

	else

		vmcb->control.virt_ext &= ~LBR_CTL_ENABLE_MASK;



	run_guest(vmcb, svm->vmcb_gpa);

	GUEST_ASSERT(svm->vmcb->control.exit_code == SVM_EXIT_VMMCALL);



	/* Trigger save/restore one more time before checking, just for kicks */

	GUEST_SYNC(true);



	/*

	 * If LBR_CTL_ENABLE is set, L1 and L2 should have separate LBR MSRs, so

	 * expect L1's LBRs to remain intact and L2 LBRs to be in the VMCB.

	 * Otherwise, the MSRs are shared between L1 & L2 so expect L2's LBRs.

	 */

	if (nested_lbrv) {

		CHECK_BRANCH_MSRS(&l1_branch);

		CHECK_BRANCH_VMCB(&l2_branch, vmcb);

	} else {

		CHECK_BRANCH_MSRS(&l2_branch);

	}

	GUEST_DONE();

}



void test_lbrv_nested_state(bool nested_lbrv)

{

	struct kvm_x86_state *state = NULL;

	struct kvm_vcpu *vcpu;

	vm_vaddr_t svm_gva;

	struct kvm_vm *vm;

	struct ucall uc;



	pr_info("Testing with nested LBRV %s\n", nested_lbrv ? "enabled" : "disabled");



	vm = vm_create_with_one_vcpu(&vcpu, l1_guest_code);

	vcpu_alloc_svm(vm, &svm_gva);

	vcpu_args_set(vcpu, 2, svm_gva, nested_lbrv);



	for (;;) {

		vcpu_run(vcpu);

		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);

		switch (get_ucall(vcpu, &uc)) {

		case UCALL_SYNC:

			/* Save the vCPU state and restore it in a new VM on sync */

			pr_info("Guest triggered save/restore.\n");

			state = vcpu_save_state(vcpu);

			kvm_vm_release(vm);

			vcpu = vm_recreate_with_one_vcpu(vm);

			vcpu_load_state(vcpu, state);

			kvm_x86_state_cleanup(state);

			break;

		case UCALL_ABORT:

			REPORT_GUEST_ASSERT(uc);

			/* NOT REACHED */

		case UCALL_DONE:

			goto done;

		default:

			TEST_FAIL("Unknown ucall %lu", uc.cmd);

		}

	}

done:

	kvm_vm_free(vm);

}



int main(int argc, char *argv[])

{

	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_SVM));

	TEST_REQUIRE(kvm_is_lbrv_enabled());



	test_lbrv_nested_state(/*nested_lbrv=*/false);

	test_lbrv_nested_state(/*nested_lbrv=*/true);



	return 0;

}