KVM: selftests: Assert that XTILE is XSAVE-enabled

Assert that XTILE is XSAVE-enabled. check_xsave_supports_xtile() doesn't
actually check anything since its return value is not used. Add the
intended assert.

Opportunistically, move the assert to a more appropriate location:
immediately after XSETBV and remove check_xsave_supports_xtile().

Fixes: 5dc19f1c ("KVM: selftests: Convert AMX test to use X86_PROPRETY_XXX")
Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20230221163655.920289-10-mizhang@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

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

@@ -115,11 +115,6 @@ static inline void check_cpuid_xsave(void)
 	GUEST_ASSERT(this_cpu_has(X86_FEATURE_OSXSAVE));
 }
 
-static bool check_xsave_supports_xtile(void)
-{
-	return __xgetbv(0) & XFEATURE_MASK_XTILE;
-}
-
 static void check_xtile_info(void)
 {
 	GUEST_ASSERT(this_cpu_has_p(X86_PROPERTY_XSTATE_MAX_SIZE_XCR0));
@@ -166,6 +161,7 @@ static void init_regs(void)
 	xcr0 = __xgetbv(0);
 	xcr0 |= XFEATURE_MASK_XTILE;
 	__xsetbv(0x0, xcr0);
+	GUEST_ASSERT(__xgetbv(0) & XFEATURE_MASK_XTILE);
 }
 
 static void __attribute__((__flatten__)) guest_code(struct tile_config *amx_cfg,
@@ -174,7 +170,6 @@ static void __attribute__((__flatten__)) guest_code(struct tile_config *amx_cfg,
 {
 	init_regs();
 	check_cpuid_xsave();
-	check_xsave_supports_xtile();
 	check_xtile_info();
 	GUEST_SYNC(1);