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From:   Zhenzhong Duan <zhenzhong.duan@oracle.com>
To:     linux-kernel@vger.kernel.org
Cc:     x86@kernel.org, tim.c.chen@linux.intel.com,
        Zhenzhong Duan <zhenzhong.duan@oracle.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: [PATCH] x86: Don't use MWAIT if explicitly requested
Date:   Fri, 18 Oct 2019 11:45:54 +0800
Message-Id: <1571370354-17736-1-git-send-email-zhenzhong.duan@oracle.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

If 'idle=nomwait' is specified or process matching what's in
processor_idle_dmi_table, we should't use MWAIT at bootup stage before
cpuidle driver loaded, even if it's preferred by default on Intel.

Add a check so that HALT instruction is used in those cases.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 arch/x86/kernel/process.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 5e94c43..37fc577 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -667,6 +667,10 @@ static void amd_e400_idle(void)
  */
 static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
 {
+	/* Don't use MWAIT-C1 if explicitly requested */
+	if (boot_option_idle_override == IDLE_NOMWAIT)
+		return 0;
+
 	if (c->x86_vendor != X86_VENDOR_INTEL)
 		return 0;
 
-- 
1.8.3.1