x86/fpu/xstate: Warn when checking alignment of disabled xfeatures

An XSAVES component's alignment/offset is meaningful only when the
feature is enabled. Return zero and WARN_ONCE on checking alignment of
disabled features.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20200109211452.27369-4-yu-cheng.yu@intel.com

arch/x86/kernel/fpu/xstate.c

@@ -325,6 +325,13 @@ static int xfeature_is_aligned(int xfeature_nr)
 	u32 eax, ebx, ecx, edx;
 
 	CHECK_XFEATURE(xfeature_nr);
+
+	if (!xfeature_enabled(xfeature_nr)) {
+		WARN_ONCE(1, "Checking alignment of disabled xfeature %d\n",
+			  xfeature_nr);
+		return 0;
+	}
+
 	cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx);
 	/*
 	 * The value returned by ECX[1] indicates the alignment