linux-kernel - [PATCH 5.16 228/285] x86/pm: Save the MSR validity status at context setup

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Date:   Tue, 12 Apr 2022 08:31:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.16 228/285] x86/pm: Save the MSR validity status at context setup

From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>

commit 73924ec4d560257004d5b5116b22a3647661e364 upstream.

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: 7a9c2dd08ead ("x86/pm: Introduce quirk framework to save/restore extra MSR registers around suspend/resume")
Suggested-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
Acked-by: Borislav Petkov <bp@...e.de>
Cc: stable@...r.kernel.org
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/power/cpu.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -40,7 +40,8 @@ static void msr_save_context(struct save
 	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 *
 	}
 
 	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;