Presented by

  • Bhupesh Sharma

    Bhupesh Sharma

    Bhupesh Sharma works with Red Hat as a part of the RH kernel team. He has been hacking on bootloaders and kernel since past 14 years. He contributes to Linux, EFI/u-boot bootloader code base and also to user-space utilities like kexec-tools and crash-utility. He also co-maintains crash-utility tool upstream. Bringing up a Silicon (i.e. running the first SW on it) after hardware tapeout is his passion and he has interest in pre-silicon emulator and simulator design methodologies as well.


With ARMv8.2 architecture extensions becoming available in new / upcoming ARM64 CPUs, two new hardware extensions, namely - LVA (Large Virtual Addressing) and LPA (Large Physical Addressing) are also being supported in open-source software now. Starting from Linux kernel version 5.4, the 52-bit (Large) Virtual Address (VA) and Physical Address (PA) support was introduced for the ARM64 kernel. Although the kernel documentation describes these features (see [1] for more details) and how they impact the new kernels running on older CPUs (which don't support 52-bit VA extension in hardware) and the newer CPUs (which support 52-bit VA extension in hardware), it is still at-times complex for a normal user to understand the same and understand how one can "opt-in" for receiving VAs from a 52-bit space. In this talk, I explain how: A. the kernel memory layout gets "flipped" for ARM64 after the support for these features were added, B. user-space applications, especially the ones which provide debugging support (e.g. kexec-tools, makedumpfile and crash-utility) get impacted because of the same, and C. how user-space applications can "opt-in" to receiving VAs from a 52-bit space by specifying an mmap hint parameter that is larger than 48-bit. [1]. [Kernel documentation describing the memory map]