Chapter 42. Kernel

Red Hat Enterprise Linux 7.3 offers the heterogeneous memory management (HMM) feature as a Technology Preview. This feature has been added to the kernel as a helper layer for devices that want to mirror a process address space into their own memory management unit (MMU). Thus a non-CPU device processor is able to read system memory using the unified system address space. To enable this feature, add experimental_hmm=enable to the kernel command line. (BZ#1230959)

This feature provides additional security to servers running Linux containers by providing better isolation between the host and the containers. Administrators of a container are no longer able to perform administrative operations on the host, which increases security. (BZ#1138782)

As a Technology Preview, the ocrdma module and the libocrdma package support the Remote Direct Memory Access over Converged Ethernet (RoCE) functionality on all network adapters in the Oce141xx family. (BZ#1334675)

As a Technology Preview, this update adds No-IOMMU mode for virtual function I/O (VFIO) drivers. The No-IOMMU mode provides the user with full user-space I/O (UIO) access to a direct memory access (DMA)-capable device without a I/O memory management unit (IOMMU). Note that in addition to not being supported, using this mode is not secure due to the lack of I/O management provided by IOMMU. (BZ#1299662)

Red Hat Enterprise Linux 7.2 introduced the criu tool as a Technology Preview. This tool implements Checkpoint/Restore in User-space (CRIU), which can be used to freeze a running application and store it as a collection of files. Later, the application can be restored from its frozen state.

Note that the criu tool depends on Protocol Buffers, a language-neutral, platform-neutral extensible mechanism for serializing structured data. The protobuf and protobuf-c packages, which provide this dependency, were also introduced in Red Hat Enterprise Linux 7.2 as a Technology Preview.

With Red Hat Enterprise Linux 7.3, the criu packages have been upgraded to upstream version 2.3, which provides a number of bug fixes and enhancements over the previous version. Notably, criu is now available also on Red Hat Enterprise Linux for POWER, little endian.

Additionally, criu can now be used for following applications running in a Red Hat Enterprise Linux 7 runc container:

The ibmvnic Device Driver has been introduced as a Technology Preview in Red Hat Enterprise Linux 7.3 for IBM POWER architectures. vNIC (Virtual Network Interface Controller) is a new PowerVM virtual networking technology that delivers enterprise capabilities and simplifies network management. It is a high-performance, efficient technology that when combined with SR-IOV NIC provides bandwidth control Quality of Service (QoS) capabilities at the virtual NIC level. vNIC significantly reduces virtualization overhead, resulting in lower latencies and fewer server resources, including CPU and memory, required for network virtualization. (BZ#947163)

The kexec system call has been provided as a Technology Preview. This system call enables loading and booting into another kernel from the currently running kernel, thus performing the function of the boot loader from within the kernel. Hardware initialization, which is normally done during a standard system boot, is not performed during a kexec boot, which significantly reduces the time required for a reboot. (BZ#1460849)