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    Subject[PATCH v3 5/5] mm,memory_hotplug: Allow userspace to enable/disable vmemmap
    Date
    It seems that we have some users out there that want to expose all
    hotpluggable memory to userspace, so this implements a toggling mechanism
    for those users who want to disable it.

    By default, vmemmap pages mechanism is enabled.

    Signed-off-by: Oscar Salvador <osalvador@suse.de>
    ---
    drivers/base/memory.c | 33 +++++++++++++++++++++++++++++++++
    include/linux/memory_hotplug.h | 3 +++
    mm/memory_hotplug.c | 7 +++++++
    3 files changed, 43 insertions(+)

    diff --git a/drivers/base/memory.c b/drivers/base/memory.c
    index d30d0f6c8ad0..5ec6b80de9dd 100644
    --- a/drivers/base/memory.c
    +++ b/drivers/base/memory.c
    @@ -578,6 +578,35 @@ static DEVICE_ATTR_WO(soft_offline_page);
    static DEVICE_ATTR_WO(hard_offline_page);
    #endif

    +#ifdef CONFIG_SPARSEMEM_VMEMMAP
    +static ssize_t vmemmap_hotplug_show(struct device *dev,
    + struct device_attribute *attr, char *buf)
    +{
    + if (vmemmap_enabled)
    + return sprintf(buf, "enabled\n");
    + else
    + return sprintf(buf, "disabled\n");
    +}
    +
    +static ssize_t vmemmap_hotplug_store(struct device *dev,
    + struct device_attribute *attr,
    + const char *buf, size_t count)
    +{
    + if (!capable(CAP_SYS_ADMIN))
    + return -EPERM;
    +
    + if (sysfs_streq(buf, "enable"))
    + vmemmap_enabled = true;
    + else if (sysfs_streq(buf, "disable"))
    + vmemmap_enabled = false;
    + else
    + return -EINVAL;
    +
    + return count;
    +}
    +static DEVICE_ATTR_RW(vmemmap_hotplug);
    +#endif
    +
    /*
    * Note that phys_device is optional. It is here to allow for
    * differentiation between which *physical* devices each
    @@ -794,6 +823,10 @@ static struct attribute *memory_root_attrs[] = {
    &dev_attr_hard_offline_page.attr,
    #endif

    +#ifdef CONFIG_SPARSEMEM_VMEMMAP
    + &dev_attr_vmemmap_hotplug.attr,
    +#endif
    +
    &dev_attr_block_size_bytes.attr,
    &dev_attr_auto_online_blocks.attr,
    NULL
    diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
    index e1e8abf22a80..03d227d13301 100644
    --- a/include/linux/memory_hotplug.h
    +++ b/include/linux/memory_hotplug.h
    @@ -134,6 +134,9 @@ extern int arch_add_memory(int nid, u64 start, u64 size,
    struct mhp_restrictions *restrictions);
    extern u64 max_mem_size;

    +#ifdef CONFIG_SPARSEMEM_VMEMMAP
    +extern bool vmemmap_enabled;
    +#endif
    extern bool memhp_auto_online;
    /* If movable_node boot option specified */
    extern bool movable_node_enabled;
    diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
    index 09d41339cd11..5ffe5375b87c 100644
    --- a/mm/memory_hotplug.c
    +++ b/mm/memory_hotplug.c
    @@ -68,6 +68,10 @@ void put_online_mems(void)

    bool movable_node_enabled = false;

    +#ifdef CONFIG_SPARSEMEM_VMEMMAP
    +bool vmemmap_enabled __read_mostly = true;
    +#endif
    +
    #ifndef CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE
    bool memhp_auto_online;
    #else
    @@ -1108,6 +1112,9 @@ static unsigned long mhp_check_flags(unsigned long flags)
    if (!flags)
    return 0;

    + if (!vmemmap_enabled)
    + return 0;
    +
    if (flags != MHP_MEMMAP_ON_MEMORY) {
    WARN(1, "Wrong flags value (%lx). Ignoring flags.\n", flags);
    return 0;
    --
    2.12.3
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