KVM: selftests: Assert that XTILE_DATA is set in IA32_XFD on #NM

Add an extra check to IA32_XFD to ensure that XTILE_DATA is actually set,
i.e. is consistent with the AMX architecture. In addition, repeat the
checks after the guest/host world switch to ensure the values of IA32_XFD
and IA32_XFD_ERR are well preserved.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20230221163655.920289-7-mizhang@google.com
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: mzhang3579

tools/testing/selftests/kvm/x86_64/amx_test.c

@@ -218,8 +218,10 @@ void guest_nm_handler(struct ex_regs *regs)
 	GUEST_SYNC(7);
 	GUEST_ASSERT(!(get_cr0() & X86_CR0_TS));
 	GUEST_ASSERT(rdmsr(MSR_IA32_XFD_ERR) == XFEATURE_MASK_XTILEDATA);
+	GUEST_ASSERT(rdmsr(MSR_IA32_XFD) == XFEATURE_MASK_XTILEDATA);
 	GUEST_SYNC(8);
 	GUEST_ASSERT(rdmsr(MSR_IA32_XFD_ERR) == XFEATURE_MASK_XTILEDATA);
+	GUEST_ASSERT(rdmsr(MSR_IA32_XFD) == XFEATURE_MASK_XTILEDATA);
 	/* Clear xfd_err */
 	wrmsr(MSR_IA32_XFD_ERR, 0);
 	/* xfd=0, enable amx */