[RFC PATCH 1/2] libnvdimm: Add prctl control for disabling synchronous fault support.

[Aneesh Kumar K.V]

Hi,


Thanks Michal. I also missed Jeff in this email thread.

-aneesh

On 5/29/20 3:03 PM, Michal Suchánek wrote:
> Adding Jan
> 
> On Fri, May 29, 2020 at 11:11:39AM +0530, Aneesh Kumar K.V wrote:
>> With POWER10, architecture is adding new pmem flush and sync instructions.
>> The kernel should prevent the usage of MAP_SYNC if applications are not using
>> the new instructions on newer hardware.
>>
>> This patch adds a prctl option MAP_SYNC_ENABLE that can be used to enable
>> the usage of MAP_SYNC. The kernel config option is added to allow the user
>> to control whether MAP_SYNC should be enabled by default or not.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
>> ---
>>   include/linux/sched/coredump.h | 13 ++++++++++---
>>   include/uapi/linux/prctl.h     |  3 +++
>>   kernel/fork.c                  |  8 +++++++-
>>   kernel/sys.c                   | 18 ++++++++++++++++++
>>   mm/Kconfig                     |  3 +++
>>   mm/mmap.c                      |  4 ++++
>>   6 files changed, 45 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
>> index ecdc6542070f..9ba6b3d5f991 100644
>> --- a/include/linux/sched/coredump.h
>> +++ b/include/linux/sched/coredump.h
>> @@ -72,9 +72,16 @@ static inline int get_dumpable(struct mm_struct *mm)
>>   #define MMF_DISABLE_THP		24	/* disable THP for all VMAs */
>>   #define MMF_OOM_VICTIM		25	/* mm is the oom victim */
>>   #define MMF_OOM_REAP_QUEUED	26	/* mm was queued for oom_reaper */
>> -#define MMF_DISABLE_THP_MASK	(1 << MMF_DISABLE_THP)
>> +#define MMF_DISABLE_MAP_SYNC	27	/* disable THP for all VMAs */
>> +#define MMF_DISABLE_THP_MASK		(1 << MMF_DISABLE_THP)
>> +#define MMF_DISABLE_MAP_SYNC_MASK	(1 << MMF_DISABLE_MAP_SYNC)
>>   
>> -#define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\
>> -				 MMF_DISABLE_THP_MASK)
>> +#define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK | \
>> +			MMF_DISABLE_THP_MASK | MMF_DISABLE_MAP_SYNC_MASK)
>> +
>> +static inline bool map_sync_enabled(struct mm_struct *mm)
>> +{
>> +	return !(mm->flags & MMF_DISABLE_MAP_SYNC_MASK);
>> +}
>>   
>>   #endif /* _LINUX_SCHED_COREDUMP_H */
>> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
>> index 07b4f8131e36..ee4cde32d5cf 100644
>> --- a/include/uapi/linux/prctl.h
>> +++ b/include/uapi/linux/prctl.h
>> @@ -238,4 +238,7 @@ struct prctl_mm_map {
>>   #define PR_SET_IO_FLUSHER		57
>>   #define PR_GET_IO_FLUSHER		58
>>   
>> +#define PR_SET_MAP_SYNC_ENABLE		59
>> +#define PR_GET_MAP_SYNC_ENABLE		60
>> +
>>   #endif /* _LINUX_PRCTL_H */
>> diff --git a/kernel/fork.c b/kernel/fork.c
>> index 8c700f881d92..d5a9a363e81e 100644
>> --- a/kernel/fork.c
>> +++ b/kernel/fork.c
>> @@ -963,6 +963,12 @@ __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
>>   
>>   static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
>>   
>> +#ifdef CONFIG_ARCH_MAP_SYNC_DISABLE
>> +unsigned long default_map_sync_mask = MMF_DISABLE_MAP_SYNC_MASK;
>> +#else
>> +unsigned long default_map_sync_mask = 0;
>> +#endif
>> +
>>   static int __init coredump_filter_setup(char *s)
>>   {
>>   	default_dump_filter =
>> @@ -1039,7 +1045,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
>>   		mm->flags = current->mm->flags & MMF_INIT_MASK;
>>   		mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
>>   	} else {
>> -		mm->flags = default_dump_filter;
>> +		mm->flags = default_dump_filter | default_map_sync_mask;
>>   		mm->def_flags = 0;
>>   	}
>>   
>> diff --git a/kernel/sys.c b/kernel/sys.c
>> index d325f3ab624a..f6127cf4128b 100644
>> --- a/kernel/sys.c
>> +++ b/kernel/sys.c
>> @@ -2450,6 +2450,24 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>>   			clear_bit(MMF_DISABLE_THP, &me->mm->flags);
>>   		up_write(&me->mm->mmap_sem);
>>   		break;
>> +
>> +	case PR_GET_MAP_SYNC_ENABLE:
>> +		if (arg2 || arg3 || arg4 || arg5)
>> +			return -EINVAL;
>> +		error = !test_bit(MMF_DISABLE_MAP_SYNC, &me->mm->flags);
>> +		break;
>> +	case PR_SET_MAP_SYNC_ENABLE:
>> +		if (arg3 || arg4 || arg5)
>> +			return -EINVAL;
>> +		if (down_write_killable(&me->mm->mmap_sem))
>> +			return -EINTR;
>> +		if (arg2)
>> +			clear_bit(MMF_DISABLE_MAP_SYNC, &me->mm->flags);
>> +		else
>> +			set_bit(MMF_DISABLE_MAP_SYNC, &me->mm->flags);
>> +		up_write(&me->mm->mmap_sem);
>> +		break;
>> +
>>   	case PR_MPX_ENABLE_MANAGEMENT:
>>   	case PR_MPX_DISABLE_MANAGEMENT:
>>   		/* No longer implemented: */
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index c1acc34c1c35..38fd7cfbfca8 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -867,4 +867,7 @@ config ARCH_HAS_HUGEPD
>>   config MAPPING_DIRTY_HELPERS
>>           bool
>>   
>> +config ARCH_MAP_SYNC_DISABLE
>> +	bool
>> +
>>   endmenu
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index f609e9ec4a25..613e5894f178 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -1464,6 +1464,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
>>   		case MAP_SHARED_VALIDATE:
>>   			if (flags & ~flags_mask)
>>   				return -EOPNOTSUPP;
>> +
>> +			if ((flags & MAP_SYNC)  && !map_sync_enabled(mm))
>> +				return -EOPNOTSUPP;
>> +
>>   			if (prot & PROT_WRITE) {
>>   				if (!(file->f_mode & FMODE_WRITE))
>>   					return -EACCES;
>> -- 
>> 2.26.2
>>