[PATCH 1/7] x86/mce: Provide a lockless memory pool to save error records

[Borislav Petkov <bp@suse.de>]

From: "Chen, Gong" <gong.chen@linux.intel.com>

printk() is not safe to use in MCE context. Add a lockless memory
allocator pool to save error records in MCE context. Those records will
be issued later, in a printk-safe context. The idea is inspired by
the APEI/GHES driver.

We're very conservative and allocate only two pages for it but since
we're going to use those pages throughout the system's lifetime, we
allocate them statically to avoid early boot time allocation woes.

Signed-off-by: Chen, Gong <gong.chen@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/1432150538-3120-2-git-send-email-gong.chen@linux.intel.com
[ Rewrite. ]
Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/Kconfig                          |  1 +
 arch/x86/include/uapi/asm/mce.h           |  3 +-
 arch/x86/kernel/cpu/mcheck/Makefile       |  2 +-
 arch/x86/kernel/cpu/mcheck/mce-genpool.c  | 99 +++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/mcheck/mce-internal.h | 12 ++++
 arch/x86/kernel/cpu/mcheck/mce.c          |  8 ++-
 6 files changed, 122 insertions(+), 3 deletions(-)
 create mode 100644 arch/x86/kernel/cpu/mcheck/mce-genpool.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 55bced17dc95..94cc6ed861be 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -949,6 +949,7 @@ config X86_REROUTE_FOR_BROKEN_BOOT_IRQS
 
 config X86_MCE
 	bool "Machine Check / overheating reporting"
+	select GENERIC_ALLOCATOR
 	default y
 	---help---
 	  Machine Check support allows the processor to notify the
diff --git a/arch/x86/include/uapi/asm/mce.h b/arch/x86/include/uapi/asm/mce.h
index a0eab85ce7b8..76880ede9a35 100644
--- a/arch/x86/include/uapi/asm/mce.h
+++ b/arch/x86/include/uapi/asm/mce.h
@@ -15,7 +15,8 @@ struct mce {
 	__u64 time;	/* wall time_t when error was detected */
 	__u8  cpuvendor;	/* cpu vendor as encoded in system.h */
 	__u8  inject_flags;	/* software inject flags */
-	__u16  pad;
+	__u8  severity;
+	__u8  usable_addr;
 	__u32 cpuid;	/* CPUID 1 EAX */
 	__u8  cs;		/* code segment */
 	__u8  bank;	/* machine check bank */
diff --git a/arch/x86/kernel/cpu/mcheck/Makefile b/arch/x86/kernel/cpu/mcheck/Makefile
index bb34b03af252..a3311c886194 100644
--- a/arch/x86/kernel/cpu/mcheck/Makefile
+++ b/arch/x86/kernel/cpu/mcheck/Makefile
@@ -1,4 +1,4 @@
-obj-y				=  mce.o mce-severity.o
+obj-y				=  mce.o mce-severity.o mce-genpool.o
 
 obj-$(CONFIG_X86_ANCIENT_MCE)	+= winchip.o p5.o
 obj-$(CONFIG_X86_MCE_INTEL)	+= mce_intel.o
diff --git a/arch/x86/kernel/cpu/mcheck/mce-genpool.c b/arch/x86/kernel/cpu/mcheck/mce-genpool.c
new file mode 100644
index 000000000000..d32e262a6d0b
--- /dev/null
+++ b/arch/x86/kernel/cpu/mcheck/mce-genpool.c
@@ -0,0 +1,99 @@
+/*
+ * MCE event pool management in MCE context
+ *
+ * Copyright (C) 2015 Intel Corp.
+ * Author: Chen, Gong <gong.chen@linux.intel.com>
+ *
+ * This file is licensed under GPLv2.
+ */
+#include <linux/smp.h>
+#include <linux/mm.h>
+#include <linux/genalloc.h>
+#include <linux/llist.h>
+#include "mce-internal.h"
+
+/*
+ * printk() is not safe in MCE context. This is a lock-less memory allocator
+ * used to save error information organized in a lock-less list.
+ *
+ * This memory pool is only to be used to save MCE records in MCE context.
+ * MCE events are rare so a fixed size memory pool should be enough. Use
+ * 2 pages to save MCE events for now (~80 MCE records at most).
+ */
+#define MCE_POOLSZ	(2 * PAGE_SIZE)
+
+static struct gen_pool *mce_evt_pool;
+static LLIST_HEAD(mce_event_llist);
+static char genpool_buf[MCE_POOLSZ];
+
+void mce_genpool_process(void)
+{
+	struct llist_node *head;
+	struct mce_evt_llist *node;
+	struct mce *mce;
+
+	head = llist_del_all(&mce_event_llist);
+	if (!head)
+		return;
+
+	head = llist_reverse_order(head);
+	llist_for_each_entry(node, head, llnode) {
+		mce = &node->mce;
+		atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, mce);
+		gen_pool_free(mce_evt_pool, (unsigned long)node, sizeof(*node));
+	}
+}
+
+bool mce_genpool_empty(void)
+{
+	return llist_empty(&mce_event_llist);
+}
+
+bool mce_genpool_add(struct mce *mce)
+{
+	struct mce_evt_llist *node;
+
+	if (!mce_evt_pool)
+		return false;
+
+	node = (void *)gen_pool_alloc(mce_evt_pool, sizeof(*node));
+	if (!node) {
+		pr_warn_ratelimited("MCE records pool full!\n");
+		return false;
+	}
+
+	memcpy(&node->mce, mce, sizeof(*mce));
+	llist_add(&node->llnode, &mce_event_llist);
+
+	return true;
+}
+
+static int mce_genpool_create(void)
+{
+	struct gen_pool *tmpp;
+	int ret = -ENOMEM;
+
+	tmpp = gen_pool_create(ilog2(sizeof(struct mce_evt_llist)), -1);
+	if (!tmpp)
+		goto out;
+
+	ret = gen_pool_add(tmpp, (unsigned long)genpool_buf, MCE_POOLSZ, -1);
+	if (ret) {
+		gen_pool_destroy(tmpp);
+		goto out;
+	}
+
+	mce_evt_pool = tmpp;
+
+out:
+	return ret;
+}
+
+int mce_genpool_init(void)
+{
+	/* Just init mce_genpool once. */
+	if (mce_evt_pool)
+		return 0;
+
+	return mce_genpool_create();
+}
diff --git a/arch/x86/kernel/cpu/mcheck/mce-internal.h b/arch/x86/kernel/cpu/mcheck/mce-internal.h
index fe32074b865b..70d43f541bed 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-internal.h
+++ b/arch/x86/kernel/cpu/mcheck/mce-internal.h
@@ -13,6 +13,8 @@ enum severity_level {
 	MCE_PANIC_SEVERITY,
 };
 
+extern struct atomic_notifier_head x86_mce_decoder_chain;
+
 #define ATTR_LEN		16
 #define INITIAL_CHECK_INTERVAL	5 * 60 /* 5 minutes */
 
@@ -24,6 +26,16 @@ struct mce_bank {
 	char			attrname[ATTR_LEN];	/* attribute name */
 };
 
+struct mce_evt_llist {
+	struct llist_node llnode;
+	struct mce mce;
+};
+
+void mce_genpool_process(void);
+bool mce_genpool_empty(void);
+bool mce_genpool_add(struct mce *mce);
+int mce_genpool_init(void);
+
 extern int (*mce_severity)(struct mce *a, int tolerant, char **msg, bool is_excp);
 struct dentry *mce_get_debugfs_dir(void);
 
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index df919ff103c3..766c4c30b5b7 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -118,7 +118,7 @@ static void (*quirk_no_way_out)(int bank, struct mce *m, struct pt_regs *regs);
  * CPU/chipset specific EDAC code can register a notifier call here to print
  * MCE errors in a human-readable form.
  */
-static ATOMIC_NOTIFIER_HEAD(x86_mce_decoder_chain);
+ATOMIC_NOTIFIER_HEAD(x86_mce_decoder_chain);
 
 /* Do initial initialization of a struct mce */
 void mce_setup(struct mce *m)
@@ -1731,6 +1731,12 @@ void mcheck_cpu_init(struct cpuinfo_x86 *c)
 		return;
 	}
 
+	if (mce_genpool_init()) {
+		mca_cfg.disabled = true;
+		pr_emerg("Couldn't allocate MCE records pool!\n");
+		return;
+	}
+
 	machine_check_vector = do_machine_check;
 
 	__mcheck_cpu_init_generic();
-- 
1.9.0.258.g00eda23