linux-kernel - [PATCH v8 8/9] x86/mtrr: Avoid repeated save of MTRRs on boot-time CPU bringup

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Date:   Thu,  9 Feb 2023 15:41:55 +0000
From:   Usama Arif <usama.arif@...edance.com>
To:     dwmw2@...radead.org, tglx@...utronix.de, kim.phillips@....com
Cc:     arjan@...ux.intel.com, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, x86@...nel.org,
        pbonzini@...hat.com, paulmck@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rcu@...r.kernel.org, mimoja@...oja.de, hewenliang4@...wei.com,
        thomas.lendacky@....com, seanjc@...gle.com, pmenzel@...gen.mpg.de,
        fam.zheng@...edance.com, punit.agrawal@...edance.com,
        simon.evans@...edance.com, liangma@...ngbit.com,
        David Woodhouse <dwmw@...zon.co.uk>,
        Usama Arif <usama.arif@...edance.com>
Subject: [PATCH v8 8/9] x86/mtrr: Avoid repeated save of MTRRs on boot-time CPU bringup

From: David Woodhouse <dwmw@...zon.co.uk>

There's no need to repeatedly save the BSP's MTRRs for each AP being
brought up at boot time. And no need to use smp_call_function_single()
even for the one time they do need to be saved.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Signed-off-by: Usama Arif <usama.arif@...edance.com>
---
 arch/x86/kernel/cpu/mtrr/mtrr.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c
index 783f3210d582..b6eae3ad4414 100644
--- a/arch/x86/kernel/cpu/mtrr/mtrr.c
+++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
@@ -721,11 +721,20 @@ void __init mtrr_bp_init(void)
  */
 void mtrr_save_state(void)
 {
+	static bool mtrr_saved;
 	int first_cpu;
 
 	if (!mtrr_enabled())
 		return;
 
+	if (system_state < SYSTEM_RUNNING) {
+		if (!mtrr_saved) {
+			mtrr_save_fixed_ranges(NULL);
+			mtrr_saved = true;
+		}
+		return;
+	}
+
 	first_cpu = cpumask_first(cpu_online_mask);
 	smp_call_function_single(first_cpu, mtrr_save_fixed_ranges, NULL, 1);
 }
-- 
2.25.1