powerpc/mce: Add debugfs interface to inject MCE

To test machine check handling, add debugfs interface to inject
slb multihit errors.

To inject slb multihit:
 #echo 1 > /sys/kernel/debug/powerpc/mce_error_inject/inject_slb_multihit

Signed-off-by: Ganesh Goudar <ganeshgr@linux.ibm.com>
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

arch/powerpc/Kconfig.debug

@@ -398,3 +398,12 @@ config KASAN_SHADOW_OFFSET
 	hex
 	depends on KASAN
 	default 0xe0000000
+
+config MCE_ERROR_INJECT
+	bool "Enable MCE error injection through debugfs"
+	depends on DEBUG_FS
+	default y
+	help
+	  This option creates an mce_error_inject directory in the
+	  powerpc debugfs directory that allows limited injection of
+	  Machine Check Errors (MCEs).

arch/powerpc/sysdev/Makefile

@@ -52,3 +52,5 @@ obj-$(CONFIG_PPC_XICS)		+= xics/
 obj-$(CONFIG_PPC_XIVE)		+= xive/
 
 obj-$(CONFIG_GE_FPGA)		+= ge/
+
+obj-$(CONFIG_MCE_ERROR_INJECT)	+= mce_error_inject.o

arch/powerpc/sysdev/mce_error_inject.c

@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Machine Check Exception injection code
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/fs.h>
+#include <linux/debugfs.h>
+#include <asm/debugfs.h>
+
+static inline unsigned long get_slb_index(void)
+{
+	unsigned long index;
+
+	index = get_paca()->stab_rr;
+
+	/*
+	 * simple round-robin replacement of slb starting at SLB_NUM_BOLTED.
+	 */
+	if (index < (mmu_slb_size - 1))
+		index++;
+	else
+		index = SLB_NUM_BOLTED;
+	get_paca()->stab_rr = index;
+	return index;
+}
+
+#define slb_esid_mask(ssize)	\
+	(((ssize) == MMU_SEGSIZE_256M) ? ESID_MASK : ESID_MASK_1T)
+
+static inline unsigned long mk_esid_data(unsigned long ea, int ssize,
+					 unsigned long slot)
+{
+	return (ea & slb_esid_mask(ssize)) | SLB_ESID_V | slot;
+}
+
+#define slb_vsid_shift(ssize)	\
+	((ssize) == MMU_SEGSIZE_256M ? SLB_VSID_SHIFT : SLB_VSID_SHIFT_1T)
+
+static inline unsigned long mk_vsid_data(unsigned long ea, int ssize,
+					 unsigned long flags)
+{
+	return (get_kernel_vsid(ea, ssize) << slb_vsid_shift(ssize)) | flags |
+		((unsigned long)ssize << SLB_VSID_SSIZE_SHIFT);
+}
+
+static void insert_slb_entry(char *p, int ssize)
+{
+	unsigned long flags, entry;
+	struct paca_struct *paca;
+
+	flags = SLB_VSID_KERNEL | mmu_psize_defs[MMU_PAGE_64K].sllp;
+
+	preempt_disable();
+
+	paca = get_paca();
+
+	entry = get_slb_index();
+	asm volatile("slbmte %0,%1" :
+			: "r" (mk_vsid_data((unsigned long)p, ssize, flags)),
+			  "r" (mk_esid_data((unsigned long)p, ssize, entry))
+			: "memory");
+
+	entry = get_slb_index();
+	asm volatile("slbmte %0,%1" :
+			: "r" (mk_vsid_data((unsigned long)p, ssize, flags)),
+			  "r" (mk_esid_data((unsigned long)p, ssize, entry))
+			: "memory");
+	preempt_enable();
+	p[0] = '!';
+}
+
+static void inject_vmalloc_slb_multihit(void)
+{
+	char *p;
+
+	p = vmalloc(2048);
+	if (!p)
+		return;
+
+	insert_slb_entry(p, MMU_SEGSIZE_1T);
+	vfree(p);
+}
+
+static void inject_kmalloc_slb_multihit(void)
+{
+	char *p;
+
+	p = kmalloc(2048, GFP_KERNEL);
+	if (!p)
+		return;
+
+	insert_slb_entry(p, MMU_SEGSIZE_1T);
+	kfree(p);
+}
+
+static ssize_t inject_slb_multihit(const char __user *u_buf, size_t count)
+{
+	char buf[32];
+	size_t buf_size;
+
+	buf_size = min(count, (sizeof(buf) - 1));
+	if (copy_from_user(buf, u_buf, buf_size))
+		return -EFAULT;
+	buf[buf_size] = '\0';
+
+	if (buf[0] != '1')
+		return -EINVAL;
+
+	inject_vmalloc_slb_multihit();
+	inject_kmalloc_slb_multihit();
+	return count;
+}
+
+static ssize_t inject_write(struct file *file, const char __user *buf,
+			    size_t count, loff_t *ppos)
+{
+	static ssize_t (*func)(const char __user *, size_t);
+
+	func = file->f_inode->i_private;
+	return func(buf, count);
+}
+
+static const struct file_operations inject_fops = {
+	.write		= inject_write,
+	.llseek		= default_llseek,
+};
+
+static int mce_error_inject_setup(void)
+{
+	struct dentry *mce_error_inject_dir;
+
+	mce_error_inject_dir = debugfs_create_dir("mce_error_inject",
+						  powerpc_debugfs_root);
+
+	if (mmu_has_feature(MMU_FTR_HPTE_TABLE)) {
+		(void)debugfs_create_file("inject_slb_multihit", 0200,
+					  mce_error_inject_dir,
+					  &inject_slb_multihit,
+					  &inject_fops);
+	}
+
+	return 0;
+}
+
+device_initcall(mce_error_inject_setup);