[PATCH 2/2] KVM: selftests: Verify that L2's LMSW leaves L1-owned CR0 bits alone

[ma.mandourr@gmail.com]

From: Mahmoud Abumandour <ma.mandourr@gmail.com>

Verify that an LMSW in L2 that exits to L0 only leaves an L1-owned CR0.TS
set, and that L2 reads an L1-owned CR0.NE from the read shadow.

Assisted-by: LLM
Signed-off-by: Mahmoud Abumandour <ma.mandourr@gmail.com>
---
 .../kvm/x86/nested_exceptions_test.c          | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/tools/testing/selftests/kvm/x86/nested_exceptions_test.c b/tools/testing/selftests/kvm/x86/nested_exceptions_test.c
index f47432526e..7113018ee6 100644
--- a/tools/testing/selftests/kvm/x86/nested_exceptions_test.c
+++ b/tools/testing/selftests/kvm/x86/nested_exceptions_test.c
@@ -109,6 +109,40 @@ static void l1_svm_code(struct svm_test_data *svm)
 	GUEST_DONE();
 }
 
+static u64 l2_cr0;
+
+static void l2_lmsw_test(void)
+{
+	/* Toggle CR0.MP, which KVM intercepts and L1 doesn't. */
+	asm volatile("lmsw %w0" : : "r" (get_cr0() ^ X86_CR0_MP));
+	l2_cr0 = get_cr0();
+	asm volatile("fnop");
+	GUEST_FAIL("L2's FNOP didn't take #NM");
+}
+
+/*
+ * L1 owns CR0.TS (set) and CR0.NE, both with a read shadow of 0.  L2's LMSW
+ * must leave both alone: FNOP takes #NM and L2 reads NE as 0.
+ */
+static void vmx_run_l2_lmsw(void)
+{
+	u64 cr0 = vmread(GUEST_CR0);
+
+	vmwrite(CR0_GUEST_HOST_MASK, X86_CR0_TS | X86_CR0_NE);
+	vmwrite(CR0_READ_SHADOW, cr0 & ~(X86_CR0_TS | X86_CR0_NE));
+	vmwrite(GUEST_CR0, cr0 | X86_CR0_TS);
+	vmwrite(EXCEPTION_BITMAP, BIT(NM_VECTOR));
+	vmwrite(GUEST_RIP, (u64)l2_lmsw_test);
+	vmresume();
+
+	GUEST_ASSERT_EQ(vmread(VM_EXIT_REASON), EXIT_REASON_EXCEPTION_NMI);
+	GUEST_ASSERT_EQ(vmread(VM_EXIT_INTR_INFO) & 0xff, NM_VECTOR);
+	GUEST_ASSERT(!(l2_cr0 & X86_CR0_NE));
+
+	vmwrite(CR0_GUEST_HOST_MASK, 0);
+	vmwrite(GUEST_CR0, cr0);
+}
+
 static void vmx_run_l2(void *l2_code, int vector, u32 error_code)
 {
 	vmwrite(GUEST_RIP, (u64)l2_code);
@@ -149,6 +183,8 @@ static void l1_vmx_code(struct vmx_pages *vmx)
 	vmwrite(EXCEPTION_BITMAP, INTERCEPT_SS_DF);
 	vmx_run_l2(l2_ss_injected_df_test, DF_VECTOR, DF_ERROR_CODE);
 
+	vmx_run_l2_lmsw();
+
 	vmwrite(EXCEPTION_BITMAP, INTERCEPT_SS);
 	vmx_run_l2(l2_ss_injected_tf_test, FAKE_TRIPLE_FAULT_VECTOR, 0);
 	GUEST_ASSERT_EQ(vmread(VM_EXIT_REASON), EXIT_REASON_TRIPLE_FAULT);
-- 
2.25.1