CONFIG_ZONE_DEVICE: Device memory (pmem, HMM, etc...) hotplug support

General informations

The Linux kernel configuration item CONFIG_ZONE_DEVICE has multiple definitions:

Device memory (pmem, HMM, etc...) hotplug support found in mm/Kconfig

The configuration item CONFIG_ZONE_DEVICE:

• prompt: Device memory (pmem, HMM, etc...) hotplug support
• type: bool
• depends on: ( CONFIG_MEMORY_HOTPLUG ) && ( CONFIG_MEMORY_HOTREMOVE ) && ( CONFIG_SPARSEMEM_VMEMMAP )
• defined in mm/Kconfig
• found in Linux kernels: 4.14–4.20, 5.0–5.19, 6.0–6.18, 6.19-rc+HEAD

Help text

Device memory hotplug support allows for establishing pmem, or other device driver discovered memory regions, in the memmap. This allows pfn_to_page() lookups of otherwise "device-physical" addresses which is needed for DAX, PCI_P2PDMA, and DEVICE_PRIVATE features among others.

Enabling this option will reduce the entropy of x86 KASLR memory regions. For example - on a 46 bit system, the entropy goes down from 16 bits to 15 bits. The actual reduction in entropy depends on the physical address bits, on processor features, kernel config (5 level page table) and physical memory present on the system.

Device memory (pmem, etc...) hotplug support found in mm/Kconfig

The configuration item CONFIG_ZONE_DEVICE:

• prompt: Device memory (pmem, etc...) hotplug support
• type: bool
• depends on: ( CONFIG_MEMORY_HOTPLUG ) && ( CONFIG_MEMORY_HOTREMOVE ) && ( CONFIG_SPARSEMEM_VMEMMAP ) && ( CONFIG_ARCH_HAS_ZONE_DEVICE )
• defined in mm/Kconfig
• found in Linux kernels: 4.3–4.13

Help text

Device memory hotplug support allows for establishing pmem, or other device driver discovered memory regions, in the memmap. This allows pfn_to_page() lookups of otherwise "device-physical" addresses which is needed for using a DAX mapping in an O_DIRECT operation, among other things.

If FS_DAX is enabled, then say Y.

Hardware

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The data is retrived from:

• Linux kernel
• Linux Kernel Driver DataBase (LKDDb)

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