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McKenney" , Thomas Huth , Andrew Morton , Steven Rostedt , "Borislav Petkov (AMD)" , Ard Biesheuvel , Greg Kroah-Hartman , Pasha Tatashin , Mike Rapoport , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, Jun 25, 2025 at 11:16=E2=80=AFPM Ira Weiny wr= ote: > > Michal Clapinski wrote: > > This includes: > > 1. Splitting one e820 entry into many regions. > > 2. Conversion to devdax during boot. > > > > This change is needed for the hypervisor live update. VMs' memory will > > be backed by those emulated pmem devices. To support various VM shapes > > I want to create devdax devices at 1GB granularity similar to hugetlb. > > Also detecting those devices as devdax during boot speeds up the whole > > process. Conversion in userspace would be much slower which is > > unacceptable while trying to minimize > > Did you explore the NFIT injection strategy which Dan suggested?[1] > > [1] https://lore.kernel.org/all/6807f0bfbe589_71fe2944d@dwillia2-xfh.jf.i= ntel.com.notmuch/ > > If so why did it not work? I'm new to all this so I might be off on some/all of the things. My issues with NFIT: 1. I can either go with custom bios or acpi nfit injection. Custom bios sounds rather aggressive to me and I'd prefer to avoid this. The NFIT injection is done via initramfs, right? If a system doesn't use initramfs at the moment, that would introduce another step in the boot process. One of the requirements of the hypervisor live update project is that the boot process has to be blazing fast and I'm worried introducing initramfs would go against this requirement. 2. If I were to create an NFIT, it would have to contain thousands of entries. That would have to be parsed on every boot. Again, I'm worried about the performance. Do you think an NFIT solution could be as fast as the simple command line solution? [snip]