[PATCH v4 21/21] KVM: x86: selftests: Add APX state handling and XCR0 sanity checks

["Chang S. Bae" <chang.seok.bae@intel.com>]

Now that KVM exposes the APX feature to guests, extend some existing
selftests to validate XCR0 configuration and state management.

Since APX repurposes the XSAVE area previously used by MPX in the
non-compacted format, add a check to ensure that MPX states are not set
when APX is enabled.

Also, load non-init APX state data in the guest so that XSTATE_BV[APX] is
set, allowing validation of APX state testing.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
---
 tools/testing/selftests/kvm/x86/state_test.c  |  3 +++
 .../selftests/kvm/x86/xcr0_cpuid_test.c       | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/tools/testing/selftests/kvm/x86/state_test.c b/tools/testing/selftests/kvm/x86/state_test.c
index 409c6cc9f921..7d93d62fc6a5 100644
--- a/tools/testing/selftests/kvm/x86/state_test.c
+++ b/tools/testing/selftests/kvm/x86/state_test.c
@@ -171,6 +171,9 @@ static void __attribute__((__flatten__)) guest_code(void *arg)
 			asm volatile ("vmovupd %0, %%zmm16" :: "m" (buffer));
 		}
 
+		if (supported_xcr0 & XFEATURE_MASK_APX)
+			write_egpr(16, 0xcccccccc);
+
 		if (this_cpu_has(X86_FEATURE_MPX)) {
 			u64 bounds[2] = { 10, 0xffffffffull };
 			u64 output[2] = { };
diff --git a/tools/testing/selftests/kvm/x86/xcr0_cpuid_test.c b/tools/testing/selftests/kvm/x86/xcr0_cpuid_test.c
index 40dc9e6b3fad..f74978ef5951 100644
--- a/tools/testing/selftests/kvm/x86/xcr0_cpuid_test.c
+++ b/tools/testing/selftests/kvm/x86/xcr0_cpuid_test.c
@@ -46,6 +46,20 @@ do {									\
 		       __supported, (xfeatures));			\
 } while (0)
 
+/*
+ * Verify that mutually exclusive architectural features do not overlap.
+ * For example, APX and MPX must never be reported as supported together.
+ */
+#define ASSERT_XFEATURE_CONFLICT(supported_xcr0, xfeatures, conflicts)			\
+do {											\
+	uint64_t __supported = (supported_xcr0) & ((xfeatures) | (conflicts));		\
+											\
+	__GUEST_ASSERT((__supported & (xfeatures)) != (xfeatures) ||			\
+		       !(__supported & (conflicts)),					\
+		       "supported = 0x%lx, xfeatures = 0x%llx, conflicts = 0x%llx",	\
+		       __supported, (xfeatures), (conflicts));				\
+} while (0)
+
 static void guest_code(void)
 {
 	u64 initial_xcr0;
@@ -79,6 +93,11 @@ static void guest_code(void)
 	ASSERT_ALL_OR_NONE_XFEATURE(supported_xcr0,
 				    XFEATURE_MASK_XTILE);
 
+	/* Check APX by ensuring MPX is not exposed concurrently */
+	ASSERT_XFEATURE_CONFLICT(supported_xcr0,
+				 XFEATURE_MASK_APX,
+				 XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);
+
 	vector = xsetbv_safe(0, XFEATURE_MASK_FP);
 	__GUEST_ASSERT(!vector,
 		       "Expected success on XSETBV(FP), got %s",
-- 
2.51.0