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Now that s390 code is prepared for memory devices that reside above the maximum storage increment exposed through SCLP, everything is in place to unlock virtio-mem support. As virtio-mem in Linux currently supports logically onlining/offlining memory in pageblock granularity, we have an effective hot(un)plug granularity of 1 MiB on s390. As virito-mem adds/removes individual Linux memory blocks (256MB), we will currently never use gigantic pages in the identity mapping. It is worth noting that neither storage keys nor storage attributes (e.g., data / nodat) are touched when onlining memory blocks, which is good because we are not supposed to touch these parts for unplugged device blocks that are logically offline in Linux. We will currently never initialize storage keys for virtio-mem memory -- IOW, storage_key_init_range() is never called. It could be added in the future when plugging device blocks. But as that function essentially does nothing without modifying the code (changing PAGE_DEFAULT_ACC), that's just fine for now. kexec should work as intended and just like on other architectures that support virtio-mem: we will never place kexec binaries on virtio-mem memory, and never indicate virtio-mem memory to the 2nd kernel. The device driver in the 2nd kernel can simply reset the device -- turning all memory unplugged, to then start plugging memory and adding them to Linux, without causing trouble because the memory is already used elsewhere. The special s390 kdump mode, whereby the 2nd kernel creates the ELF core header, won't currently dump virtio-mem memory. The virtio-mem driver has a special kdump mode, from where we can detect memory ranges to dump. Based on this, support for dumping virtio-mem memory can be added in the future fairly easily. Acked-by: Michael S. Tsirkin <mst@redhat.com> Tested-by: Mario Casquero <mcasquer@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Heiko Carstens <hca@linux.ibm.com> Tested-by: Sumanth Korikkar <sumanthk@linux.ibm.com> Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com> Link: https://lore.kernel.org/r/20241025141453.1210600-5-david@redhat.com Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.