linux-kernel - [PATCH v5 05/19] x86/mce: WARN once if IA32_FEAT

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Date:   Fri, 20 Dec 2019 20:44:59 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Tony Luck <tony.luck@...el.com>,
        Tony W Wang-oc <TonyWWang-oc@...oxin.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Len Brown <lenb@...nel.org>, Shuah Khan <shuah@...nel.org>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-edac@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kselftest@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Subject: [PATCH v5 05/19] x86/mce: WARN once if IA32_FEAT_CTL MSR is left unlocked

WARN if the IA32_FEAT_CTL MSR is somehow left unlocked now that CPU
initialization unconditionally locks the MSR.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kernel/cpu/mce/intel.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/intel.c b/arch/x86/kernel/cpu/mce/intel.c
index c238518b84a2..5627b1091b85 100644
--- a/arch/x86/kernel/cpu/mce/intel.c
+++ b/arch/x86/kernel/cpu/mce/intel.c
@@ -116,14 +116,15 @@ static bool lmce_supported(void)
 	/*
 	 * BIOS should indicate support for LMCE by setting bit 20 in
 	 * IA32_FEAT_CTL without which touching MCG_EXT_CTL will generate a #GP
-	 * fault.
+	 * fault.  The MSR must also be locked for LMCE_ENABLED to take effect.
+	 * WARN if the MSR isn't locked as init_ia32_feat_ctl() unconditionally
+	 * locks the MSR in the event that it wasn't already locked by BIOS.
 	 */
 	rdmsrl(MSR_IA32_FEAT_CTL, tmp);
-	if ((tmp & (FEAT_CTL_LOCKED | FEAT_CTL_LMCE_ENABLED)) ==
-		   (FEAT_CTL_LOCKED | FEAT_CTL_LMCE_ENABLED))
-		return true;
+	if (WARN_ON_ONCE(!(tmp & FEAT_CTL_LOCKED)))
+		return false;
 
-	return false;
+	return tmp & FEAT_CTL_LMCE_ENABLED;
 }
 
 bool mce_intel_cmci_poll(void)
-- 
2.24.1