Re: [PATCH v4 03/12] mm: Introduce memfile_notifier

[Vlastimil Babka]

On 1/18/22 14:21, Chao Peng wrote:
> This patch introduces memfile_notifier facility so existing memory file
> subsystems (e.g. tmpfs/hugetlbfs) can provide memory pages to allow a
> third kernel component to make use of memory bookmarked in the memory
> file and gets notified when the pages in the memory file become
> allocated/invalidated.
> 
> It will be used for KVM to use a file descriptor as the guest memory
> backing store and KVM will use this memfile_notifier interface to
> interact with memory file subsystems. In the future there might be other
> consumers (e.g. VFIO with encrypted device memory).
> 
> It consists two sets of callbacks:
>   - memfile_notifier_ops: callbacks for memory backing store to notify
>     KVM when memory gets allocated/invalidated.
>   - memfile_pfn_ops: callbacks for KVM to call into memory backing store
>     to request memory pages for guest private memory.
> 
> Userspace is in charge of guest memory lifecycle: it first allocates
> pages in memory backing store and then passes the fd to KVM and lets KVM
> register each memory slot to memory backing store via
> memfile_register_notifier.
> 
> The supported memory backing store should maintain a memfile_notifier list
> and provide routine for memfile_notifier to get the list head address and
> memfile_pfn_ops callbacks for memfile_register_notifier. It also should call
> memfile_notifier_fallocate/memfile_notifier_invalidate when the bookmarked
> memory gets allocated/invalidated.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

Process nitpick:
Here and in patch 4/12 you have Kirill's S-o-b so there should probably be
also "From: Kirill ..." as was in v3? Or in case you modified the original
patches so much to become the primary author, you should add
"Co-developed-by: Kirill ..." here before his S-o-b.

> Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> ---
>  include/linux/memfile_notifier.h | 53 +++++++++++++++++++
>  mm/Kconfig                       |  4 ++
>  mm/Makefile                      |  1 +
>  mm/memfile_notifier.c            | 89 ++++++++++++++++++++++++++++++++
>  4 files changed, 147 insertions(+)
>  create mode 100644 include/linux/memfile_notifier.h
>  create mode 100644 mm/memfile_notifier.c
> 
> diff --git a/include/linux/memfile_notifier.h b/include/linux/memfile_notifier.h
> new file mode 100644
> index 000000000000..a03bebdd1322
> --- /dev/null
> +++ b/include/linux/memfile_notifier.h
> @@ -0,0 +1,53 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_MEMFILE_NOTIFIER_H
> +#define _LINUX_MEMFILE_NOTIFIER_H
> +
> +#include <linux/rculist.h>
> +#include <linux/spinlock.h>
> +#include <linux/srcu.h>
> +#include <linux/fs.h>
> +
> +struct memfile_notifier;
> +
> +struct memfile_notifier_ops {
> +	void (*invalidate)(struct memfile_notifier *notifier,
> +			   pgoff_t start, pgoff_t end);
> +	void (*fallocate)(struct memfile_notifier *notifier,
> +			  pgoff_t start, pgoff_t end);
> +};
> +
> +struct memfile_pfn_ops {
> +	long (*get_lock_pfn)(struct inode *inode, pgoff_t offset, int *order);
> +	void (*put_unlock_pfn)(unsigned long pfn);
> +};
> +
> +struct memfile_notifier {
> +	struct list_head list;
> +	struct memfile_notifier_ops *ops;
> +};
> +
> +struct memfile_notifier_list {
> +	struct list_head head;
> +	spinlock_t lock;
> +};
> +
> +#ifdef CONFIG_MEMFILE_NOTIFIER
> +static inline void memfile_notifier_list_init(struct memfile_notifier_list *list)
> +{
> +	INIT_LIST_HEAD(&list->head);
> +	spin_lock_init(&list->lock);
> +}
> +
> +extern void memfile_notifier_invalidate(struct memfile_notifier_list *list,
> +					pgoff_t start, pgoff_t end);
> +extern void memfile_notifier_fallocate(struct memfile_notifier_list *list,
> +				       pgoff_t start, pgoff_t end);
> +extern int memfile_register_notifier(struct inode *inode,
> +				     struct memfile_notifier *notifier,
> +				     struct memfile_pfn_ops **pfn_ops);
> +extern void memfile_unregister_notifier(struct inode *inode,
> +					struct memfile_notifier *notifier);
> +
> +#endif /* CONFIG_MEMFILE_NOTIFIER */
> +
> +#endif /* _LINUX_MEMFILE_NOTIFIER_H */
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 28edafc820ad..fa31eda3c895 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -900,6 +900,10 @@ config IO_MAPPING
>  config SECRETMEM
>  	def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
>  
> +config MEMFILE_NOTIFIER
> +	bool
> +	select SRCU
> +
>  source "mm/damon/Kconfig"
>  
>  endmenu
> diff --git a/mm/Makefile b/mm/Makefile
> index d6c0042e3aa0..80588f7c3bc2 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -130,3 +130,4 @@ obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o
>  obj-$(CONFIG_IO_MAPPING) += io-mapping.o
>  obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
>  obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o
> +obj-$(CONFIG_MEMFILE_NOTIFIER) += memfile_notifier.o
> diff --git a/mm/memfile_notifier.c b/mm/memfile_notifier.c
> new file mode 100644
> index 000000000000..8171d4601a04
> --- /dev/null
> +++ b/mm/memfile_notifier.c
> @@ -0,0 +1,89 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + *  linux/mm/memfile_notifier.c
> + *
> + *  Copyright (C) 2022  Intel Corporation.
> + *             Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> + */
> +
> +#include <linux/memfile_notifier.h>
> +#include <linux/srcu.h>
> +
> +DEFINE_STATIC_SRCU(srcu);
> +
> +void memfile_notifier_invalidate(struct memfile_notifier_list *list,
> +				 pgoff_t start, pgoff_t end)
> +{
> +	struct memfile_notifier *notifier;
> +	int id;
> +
> +	id = srcu_read_lock(&srcu);
> +	list_for_each_entry_srcu(notifier, &list->head, list,
> +				 srcu_read_lock_held(&srcu)) {
> +		if (notifier->ops && notifier->ops->invalidate)
> +			notifier->ops->invalidate(notifier, start, end);
> +	}
> +	srcu_read_unlock(&srcu, id);
> +}
> +
> +void memfile_notifier_fallocate(struct memfile_notifier_list *list,
> +				pgoff_t start, pgoff_t end)
> +{
> +	struct memfile_notifier *notifier;
> +	int id;
> +
> +	id = srcu_read_lock(&srcu);
> +	list_for_each_entry_srcu(notifier, &list->head, list,
> +				 srcu_read_lock_held(&srcu)) {
> +		if (notifier->ops && notifier->ops->fallocate)
> +			notifier->ops->fallocate(notifier, start, end);
> +	}
> +	srcu_read_unlock(&srcu, id);
> +}
> +
> +static int memfile_get_notifier_info(struct inode *inode,
> +				     struct memfile_notifier_list **list,
> +				     struct memfile_pfn_ops **ops)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +int memfile_register_notifier(struct inode *inode,
> +			      struct memfile_notifier *notifier,
> +			      struct memfile_pfn_ops **pfn_ops)
> +{
> +	struct memfile_notifier_list *list;
> +	int ret;
> +
> +	if (!inode || !notifier | !pfn_ops)
> +		return -EINVAL;
> +
> +	ret = memfile_get_notifier_info(inode, &list, pfn_ops);
> +	if (ret)
> +		return ret;
> +
> +	spin_lock(&list->lock);
> +	list_add_rcu(&notifier->list, &list->head);
> +	spin_unlock(&list->lock);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(memfile_register_notifier);
> +
> +void memfile_unregister_notifier(struct inode *inode,
> +				 struct memfile_notifier *notifier)
> +{
> +	struct memfile_notifier_list *list;
> +
> +	if (!inode || !notifier)
> +		return;
> +
> +	BUG_ON(memfile_get_notifier_info(inode, &list, NULL));
> +
> +	spin_lock(&list->lock);
> +	list_del_rcu(&notifier->list);
> +	spin_unlock(&list->lock);
> +
> +	synchronize_srcu(&srcu);
> +}
> +EXPORT_SYMBOL_GPL(memfile_unregister_notifier);