x86/mtrr: Check if fixed-range MTRR exists in mtrr_save_fixed_ranges()

When suspending, save_processor_state() calls mtrr_save_fixed_ranges()
to save fixed-range MTRRs. On platforms without fixed-range MTRRs,
accessing these MSRs will trigger unchecked MSR access error. Make
sure fixed-range MTRRs are supported before access to prevent such
error.

Since mtrr_state.have_fixed is only set when MTRRs are present and
enabled, checking the CPU feature flag in mtrr_save_fixed_ranges()
is unnecessary.

Fixes: 3ebad59 ("[PATCH] x86: Save and restore the fixed-range MTRRs of the BSP when suspending")
Tracked-On: OAM-132455
Signed-off-by: Jiaqing Zhao <jiaqing.zhao@intel.com>

Author: jiaqingz-dev

arch/x86/kernel/cpu/mtrr/generic.c

@@ -591,7 +591,7 @@ static void get_fixed_ranges(mtrr_type *frs)
 
 void mtrr_save_fixed_ranges(void *info)
 {
-	if (boot_cpu_has(X86_FEATURE_MTRR))
+	if (mtrr_state.have_fixed)
 		get_fixed_ranges(mtrr_state.fixed_ranges);
 }