Re: [PATCH 2/3] powerpc/mce: Add debugfs interface to inject MCE

[Ganesh <ganeshgr@linux.ibm.com>]

On 9/17/20 5:53 PM, Michal Suchánek wrote:
> Hello,
>
> On Wed, Sep 16, 2020 at 10:52:27PM +0530, Ganesh Goudar wrote:
>> 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             |   9 ++
>>   arch/powerpc/sysdev/Makefile           |   2 +
>>   arch/powerpc/sysdev/mce_error_inject.c | 148 +++++++++++++++++++++++++
>>   3 files changed, 159 insertions(+)
>>   create mode 100644 arch/powerpc/sysdev/mce_error_inject.c
>>
>> diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
>> index b88900f4832f..61db133f2f0d 100644
>> --- a/arch/powerpc/Kconfig.debug
>> +++ b/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).
>> diff --git a/arch/powerpc/sysdev/Makefile b/arch/powerpc/sysdev/Makefile
>> index 026b3f01a991..7fc102222b77 100644
>> --- a/arch/powerpc/sysdev/Makefile
>> +++ b/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
>> diff --git a/arch/powerpc/sysdev/mce_error_inject.c b/arch/powerpc/sysdev/mce_error_inject.c
>> new file mode 100644
>> index 000000000000..ca4726bfa2d9
>> --- /dev/null
>> +++ b/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();
> This seems unused?
Thanks, ill remove it.
>> +
>> +	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();
> This is missing the test of multihit in paca which is for some reason
> special.
I will add it, Thanks
> Thanks
>
> Michal
>> +	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);
>> -- 
>> 2.26.2
>>