x86/pm: Save the MSR validity status at context setup

The mechanism to save/restore MSRs during S3 suspend/resume checks for
the MSR validity during suspend, and only restores the MSR if its a
valid MSR.  This is not optimal, as an invalid MSR will unnecessarily
throw an exception for every suspend cycle.  The more invalid MSRs,
higher the impact will be.

Check and save the MSR validity at setup.  This ensures that only valid
MSRs that are guaranteed to not throw an exception will be attempted
during suspend.

Fixes: 7a9c2dd0 ("x86/pm: Introduce quirk framework to save/restore extra MSR registers around suspend/resume")
Suggested-by: NDave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: NPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: NDave Hansen <dave.hansen@linux.intel.com>
Acked-by: NBorislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/x86/power/cpu.c

@@ -40,7 +40,8 @@ static void msr_save_context(struct saved_context *ctxt)
 	struct saved_msr *end = msr + ctxt->saved_msrs.num;
 
 	while (msr < end) {
-		msr->valid = !rdmsrl_safe(msr->info.msr_no, &msr->info.reg.q);
+		if (msr->valid)
+			rdmsrl(msr->info.msr_no, msr->info.reg.q);
 		msr++;
 	}
 }
@@ -424,8 +425,10 @@ static int msr_build_context(const u32 *msr_id, const int num)
 	}
 
 	for (i = saved_msrs->num, j = 0; i < total_num; i++, j++) {
+		u64 dummy;
+
 		msr_array[i].info.msr_no	= msr_id[j];
-		msr_array[i].valid		= false;
+		msr_array[i].valid		= !rdmsrl_safe(msr_id[j], &dummy);
 		msr_array[i].info.reg.q		= 0;
 	}
 	saved_msrs->num   = total_num;