| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <b3d435d2-643f-4dad-9928-bc7fb5080181@kernel.org>
Date: Wed, 14 Jan 2026 11:21:34 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Gregory Price <gourry@...rry.net>, linux-mm@...ck.org
Cc: linux-cxl@...r.kernel.org, nvdimm@...ts.linux.dev,
linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
kernel-team@...a.com, dan.j.williams@...el.com, vishal.l.verma@...el.com,
dave.jiang@...el.com, mst@...hat.com, jasowang@...hat.com,
xuanzhuo@...ux.alibaba.com, eperezma@...hat.com, osalvador@...e.de,
akpm@...ux-foundation.org
Subject: Re: [PATCH 3/8] mm/memory_hotplug: add APIs for explicit online type
control
On 1/14/26 09:51, Gregory Price wrote:
> Add new memory hotplug APIs that allow callers to explicitly control
> the online type when adding or managing memory:
>
> - Extend add_memory_driver_managed() with an online_type parameter:
> Callers can now specify MMOP_ONLINE, MMOP_ONLINE_KERNEL, or
> MMOP_ONLINE_MOVABLE to online with that type, MMOP_OFFLINE to leave
> memory offline, or MMOP_SYSTEM_DEFAULT to use the system default
> policy. Update virtio_mem to pass MMOP_SYSTEM_DEFAULT to maintain
> existing behavior.
I wonder if we rather want to add a new interface
(add_and_online_memory_driver_managed()) where we can restrict it to
known kernel modules that do not violate user-space onlining policies.
For dax we know that user space will define the policy.
>
> - online_memory_range(): online a previously-added memory range with
> a specified online type (MMOP_ONLINE, MMOP_ONLINE_KERNEL, or
> MMOP_ONLINE_MOVABLE). Validates that the type is valid for onlining.
Why not simply online_memory() and offline_memory() ?
>
> - offline_memory(): offline a memory range without removing it. This
> is a wrapper around the internal __offline_memory() that handles
> locking. Useful for drivers that want to offline memory blocks
> before performing other operations.
>
These two should be not exported to arbitrary kernel modules. Use
EXPORT_SYMBOL_FOR_MODULES() if required, or do not export them at all.
> These APIs enable drivers like dax_kmem to implement sophisticated
> memory management policies, such as adding memory offline and deferring
> the online decision to userspace.
>
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
> drivers/dax/kmem.c | 3 +-
> drivers/virtio/virtio_mem.c | 3 +-
> include/linux/memory_hotplug.h | 4 ++-
> mm/memory_hotplug.c | 63 ++++++++++++++++++++++++++++++++--
> 4 files changed, 68 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index c036e4d0b610..5e0cf94a9620 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -175,7 +175,8 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> * this as RAM automatically.
> */
> rc = add_memory_driver_managed(data->mgid, range.start,
> - range_len(&range), kmem_name, mhp_flags);
> + range_len(&range), kmem_name, mhp_flags,
> + MMOP_SYSTEM_DEFAULT);
>
> if (rc) {
> dev_warn(dev, "mapping%d: %#llx-%#llx memory add failed\n",
> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
> index 1688ecd69a04..b1ec8f2b9e31 100644
> --- a/drivers/virtio/virtio_mem.c
> +++ b/drivers/virtio/virtio_mem.c
> @@ -654,7 +654,8 @@ static int virtio_mem_add_memory(struct virtio_mem *vm, uint64_t addr,
> /* Memory might get onlined immediately. */
> atomic64_add(size, &vm->offline_size);
> rc = add_memory_driver_managed(vm->mgid, addr, size, vm->resource_name,
> - MHP_MERGE_RESOURCE | MHP_NID_IS_MGID);
> + MHP_MERGE_RESOURCE | MHP_NID_IS_MGID,
> + MMOP_SYSTEM_DEFAULT);
> if (rc) {
> atomic64_sub(size, &vm->offline_size);
> dev_warn(&vm->vdev->dev, "adding memory failed: %d\n", rc);
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index d5407264d72a..0f98bea6da65 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -265,6 +265,7 @@ static inline void pgdat_resize_init(struct pglist_data *pgdat) {}
> extern void try_offline_node(int nid);
> extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages,
> struct zone *zone, struct memory_group *group);
> +extern int offline_memory(u64 start, u64 size);
No new "extern" for functions.
> extern int remove_memory(u64 start, u64 size);
> extern void __remove_memory(u64 start, u64 size);
> extern int offline_and_remove_memory(u64 start, u64 size);
> @@ -297,7 +298,8 @@ extern int add_memory_resource(int nid, struct resource *resource,
> mhp_t mhp_flags);
> extern int add_memory_driver_managed(int nid, u64 start, u64 size,
> const char *resource_name,
> - mhp_t mhp_flags);
> + mhp_t mhp_flags, int online_type);
> +extern int online_memory_range(u64 start, u64 size, int online_type);
> extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
> unsigned long nr_pages,
> struct vmem_altmap *altmap, int migratetype,
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index ab73c8fcc0f1..515ff9d18039 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1343,6 +1343,34 @@ static int online_memory_block(struct memory_block *mem, void *arg)
> return device_online(&mem->dev);
> }
>
> +/**
> + * online_memory_range - online memory blocks in a range
> + * @start: physical start address of memory region
> + * @size: size of memory region
> + * @online_type: MMOP_ONLINE, MMOP_ONLINE_KERNEL, or MMOP_ONLINE_MOVABLE
I wonder if we instead want something that consumes all parameters like
int online_or_offline_memory(int online_type)
Then it's easier to use and we don't really have to document the
"online_type" that much to hand-select some values.
(I'm sure there are better nameing suggestions :) )
Should we document what happens if the memory is already online, but was
onlined to a different zone?
> + *
> + * Online all memory blocks in the specified range with the given online type.
> + * The memory must have already been added to the system.
> + *
> + * Returns 0 on success, negative error code on failure.
> + */
> +int online_memory_range(u64 start, u64 size, int online_type)
> +{
> + int rc;
> +
> + if (online_type == MMOP_OFFLINE ||
> + online_type > MMOP_ONLINE_MOVABLE)
> + return -EINVAL;
> +
> + lock_device_hotplug();
> + rc = walk_memory_blocks(start, size, &online_type,
> + online_memory_block);
> + unlock_device_hotplug();
> +
> + return rc;
> +}
> +EXPORT_SYMBOL_GPL(online_memory_range);
> +
> #ifndef arch_supports_memmap_on_memory
> static inline bool arch_supports_memmap_on_memory(unsigned long vmemmap_size)
> {
> @@ -1656,9 +1684,16 @@ EXPORT_SYMBOL_GPL(add_memory);
> *
> * The resource_name (visible via /proc/iomem) has to have the format
> * "System RAM ($DRIVER)".
> + *
> + * @online_type specifies the online behavior: MMOP_ONLINE, MMOP_ONLINE_KERNEL,
> + * MMOP_ONLINE_MOVABLE to online with that type, MMOP_OFFLINE to leave offline,
> + * or MMOP_SYSTEM_DEFAULT to use the system default policy.
> + *
I think we can simplify this documentation. Especially, one
MMOP_SYSTEM_DEFAULT is gone.
> + * Returns 0 on success, negative error code on failure.
> */
> int add_memory_driver_managed(int nid, u64 start, u64 size,
> - const char *resource_name, mhp_t mhp_flags)
> + const char *resource_name, mhp_t mhp_flags,
> + int online_type)
> {
> struct resource *res;
> int rc;
> @@ -1668,6 +1703,13 @@ int add_memory_driver_managed(int nid, u64 start, u64 size,
> resource_name[strlen(resource_name) - 1] != ')')
> return -EINVAL;
>
> + /* Convert system default to actual online type */
> + if (online_type == MMOP_SYSTEM_DEFAULT)
> + online_type = mhp_get_default_online_type();
> +
> + if (online_type < 0 || online_type > MMOP_ONLINE_MOVABLE)
> + return -EINVAL;
> +
> lock_device_hotplug();
>
> res = register_memory_resource(start, size, resource_name);
> @@ -1676,7 +1718,7 @@ int add_memory_driver_managed(int nid, u64 start, u64 size,
> goto out_unlock;
> }
>
> - rc = add_memory_resource(nid, res, mhp_flags);
> + rc = __add_memory_resource(nid, res, mhp_flags, online_type);
> if (rc < 0)
> release_memory_resource(res);
>
> @@ -2412,6 +2454,23 @@ static int __offline_memory(u64 start, u64 size)
> return rc;
> }
>
> +/*
> + * Try to offline a memory range. Might take a long time to finish in case
> + * memory is still in use. In case of failure, already offlined memory blocks
> + * will be re-onlined.
> + */
Proper kerneldoc? :)
> +int offline_memory(u64 start, u64 size)
> +{
> + int rc;
> +
> + lock_device_hotplug();
> + rc = __offline_memory(start, size);
> + unlock_device_hotplug();
> +
> + return rc;
> +}
> +EXPORT_SYMBOL_GPL(offline_memory);
> +
> /*
> * Try to offline and remove memory. Might take a long time to finish in case
> * memory is still in use. Primarily useful for memory devices that logically
--
Cheers
David
Powered by blists - more mailing lists