linux-kernel - [Patch V1] x86, mce: Don't clear global error reporting banks during cpu

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Message-Id: <1441391390-16985-1-git-send-email-ashok.raj@intel.com>
Date:	Fri,  4 Sep 2015 14:29:50 -0400
From:	Ashok Raj <ashok.raj@...el.com>
To:	linux-kernel@...r.kernel.org
Cc:	Ashok Raj <ashok.raj@...el.com>, Boris Petkov <bp@...e.de>,
	linux-edac@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
	Serge Ayoun <serge.ayoun@...el.com>
Subject: [Patch V1] x86, mce: Don't clear global error reporting banks during cpu_offline

During CPU offline, or during suspend/resume operations, its not safe to
clear MCi_CTL. These MSR's are either thread scoped (meaning private to
thread), or core scoped (private to threads in that core only), or socket
scope i.e visible and controllable from all threads in the socket.

When we turn off during CPU_OFFLINE, just offlining a single CPU will
stop signaling for all the socket wide resources, such as LLC, iMC for e.g.

It is true for Intel CPU's. But there seems some history that other processors
may require to turn these off during every CPU offline.

Intel Secure Guard eXtentions (SGX) is worried that it might be possible to
compromise integrity in a SGX system if the attacker has control of host system
to inject errors which would be otherwise ignored when MCi_CTL bits are
cleared. Hence on SGX enabled systems, if MCi_CTL is cleared SGX becomes not
available anymore.

- Consolidated some code to use sharing
- Minor changes to some prototypes to fit usage.
- Left handling same for non-Intel CPU models to avoid any unknown regressions.
- Fixed review comments from Boris

Signed-off-by: Ashok Raj <ashok.raj@...el.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Tested-by: Serge Ayoun <serge.ayoun@...el.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index d350858..69c7e3c 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -2100,7 +2100,7 @@ int __init mcheck_init(void)
  * Disable machine checks on suspend and shutdown. We can't really handle
  * them later.
  */
-static int mce_disable_error_reporting(void)
+static void mce_disable_error_reporting(void)
 {
 	int i;
 
@@ -2110,17 +2110,32 @@ static int mce_disable_error_reporting(void)
 		if (b->init)
 			wrmsrl(MSR_IA32_MCx_CTL(i), 0);
 	}
-	return 0;
+	return;
+}
+
+static void vendor_disable_error_reporting(void)
+{
+	/*
+	 * Don't clear on Intel CPUs. Some of these MSRs are
+	 * socket wide. Disabling them for just a single CPU offline
+	 * is bad, since it will inhibit reporting for all shared
+	 * resources.. such as LLC, iMC for e.g.
+	 */
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
+		return;
+
+	mce_disable_error_reporting();
 }
 
 static int mce_syscore_suspend(void)
 {
-	return mce_disable_error_reporting();
+	vendor_disable_error_reporting();
+	return 0;
 }
 
 static void mce_syscore_shutdown(void)
 {
-	mce_disable_error_reporting();
+	vendor_disable_error_reporting();
 }
 
 /*
@@ -2400,19 +2415,14 @@ static void mce_device_remove(unsigned int cpu)
 static void mce_disable_cpu(void *h)
 {
 	unsigned long action = *(unsigned long *)h;
-	int i;
 
 	if (!mce_available(raw_cpu_ptr(&cpu_info)))
 		return;
 
 	if (!(action & CPU_TASKS_FROZEN))
 		cmci_clear();
-	for (i = 0; i < mca_cfg.banks; i++) {
-		struct mce_bank *b = &mce_banks[i];
 
-		if (b->init)
-			wrmsrl(MSR_IA32_MCx_CTL(i), 0);
-	}
+	vendor_disable_error_reporting();
 }
 
 static void mce_reenable_cpu(void *h)
-- 
2.4.3

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