[PATCH 3/4] KVM: selftests: Add test to verify KVM allows loading XTILE data with XFD=1

[Paolo Bonzini]

Extend the AMX test to verify that loading guest state via KVM_SET_XSAVE
for a disabled component, i.e. with XSTATE_BV[i]=1 and XFD[i]=1, doesn't
cause KVM to explode.  To load the "bad" state, load XSAVE state from a
snapshot taken before setting XFD.  Take care to restore *only* XSAVE
state, as restoring GPRs will corrupt the guest and restoring MSRs will
make the test useless (because the test would revert to XFD=0).

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/x86/amx_test.c | 44 ++++++++++++++++++----
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/amx_test.c b/tools/testing/selftests/kvm/x86/amx_test.c
index ab6d8748d7b8..1d5fffddc625 100644
--- a/tools/testing/selftests/kvm/x86/amx_test.c
+++ b/tools/testing/selftests/kvm/x86/amx_test.c
@@ -128,6 +128,7 @@ enum amx_test_syncs {
 	AMX_SYNC_SAVE 		= BIT(0),
 	AMX_SYNC_RESTORE	= BIT(1),
 	AMX_SYNC_CHECK_TILEDATA	= BIT(2),
+	AMX_SYNC_RESTORE_XSTATE	= BIT(3),
 
 	AMX_SYNC_SAVE_RESTORE = AMX_SYNC_SAVE | AMX_SYNC_RESTORE,
 };
@@ -165,11 +166,19 @@ static void __attribute__((__flatten__)) guest_code(struct tile_config *amx_cfg,
 	set_tilecfg(amx_cfg);
 	__ldtilecfg(amx_cfg);
 	__tileloadd(tiledata);
-	GUEST_SYNC(AMX_SYNC_SAVE_RESTORE | AMX_SYNC_CHECK_TILEDATA);
+
+	/* Save state and check tile data, but don't restore just yet. */
+	GUEST_SYNC(AMX_SYNC_SAVE | AMX_SYNC_CHECK_TILEDATA);
 
 	/* xfd=0x40000, disable amx tiledata */
 	wrmsr(MSR_IA32_XFD, XFEATURE_MASK_XTILE_DATA);
 
+	/*
+	 * Restore the previously saved XSTATE so that the host tries setting
+	 * tiledata while guest XFD is set.
+	 */
+	GUEST_SYNC(AMX_SYNC_RESTORE_XSTATE);
+
 	/*
 	 * XTILEDATA is cleared in xstate_bv but set in xcomp_bv, this property
 	 * remains the same even when amx tiledata is disabled by IA32_XFD.
@@ -289,20 +298,41 @@ int main(int argc, char *argv[])
 			TEST_ASSERT(ret == 0, "memcmp failed, ret=%d", ret);
 		}
 
-
-		if (!(uc.args[1] & AMX_SYNC_RESTORE))
+		if (!(uc.args[1] & (AMX_SYNC_RESTORE | AMX_SYNC_RESTORE_XSTATE)))
 			continue;
 
 		TEST_ASSERT(state, "RESTORE without a SAVE");
 
+		TEST_ASSERT(!(uc.args[1] & AMX_SYNC_RESTORE) ||
+			    !(uc.args[1] & AMX_SYNC_RESTORE_XSTATE),
+			    "Only one type of restore is supported per sync");
+
 		memset(&regs1, 0, sizeof(regs1));
 		vcpu_regs_get(vcpu, &regs1);
 
-		kvm_vm_release(vm);
+		/*
+		 * Restore XSTATE from a previous snapshot, e.g. to verify that
+		 * KVM allows loading XTILE data when it's disabled via XFD.
+		 */
+		if (uc.args[1] & AMX_SYNC_RESTORE_XSTATE)
+			vcpu_xsave_set(vcpu, state->xsave);
+
+		if (uc.args[1] & AMX_SYNC_RESTORE) {
+			/*
+			 * Restoring *all* state from a previous snapshot will
+			 * corrupt the guest, e.g. GPRs and RIP, and send it
+			 * into the weeds.
+			 */
+			TEST_ASSERT(uc.args[1] & AMX_SYNC_SAVE,
+				    "Restoring an old snapshot will corrupt the guest");
+
+			kvm_vm_release(vm);
+
+			/* Restore state in a new VM.  */
+			vcpu = vm_recreate_with_one_vcpu(vm);
+			vcpu_load_state(vcpu, state);
+		}
 
-		/* Restore state in a new VM.  */
-		vcpu = vm_recreate_with_one_vcpu(vm);
-		vcpu_load_state(vcpu, state);
 		kvm_x86_state_cleanup(state);
 		state = NULL;
 
-- 
2.52.0.351.gbe84eed79e-goog


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