On Mon, 2020-07-20 at 13:51 -0300, Daniel Henrique Barboza wrote: > + <li>the remaining size (total-size - label-size), also called guest > + area, will be aligned to 4KiB as default. For pSeries guests, the > + guest area will be aligned down to 256MiB, and the minimum size > + of the guest area must be at least 256MiB plus the label-size.</li> The last part of the sentence seems contradictory: earlier you define the guest area to be the total size minus the label size, but then you say that the guest area must be at least 256MiB plus the label size. I suggest remove the trailing "plus the label-size". Are you okay with me doing that before pushing? If so, then Reviewed-by: Andrea Bolognani <abologna@xxxxxxxxxx> Anyway, while it's good to have these requirements documented, I believe we need to rethink our approach to NVDIMMs a bit, as the current behavior is confusing and full of potential pitfalls. Ideally, we'd drop the automatic alignment step which happens at guest startup time and replace it with an upfront check on the constraints: if the user tries to use a NVDIMM module that's not sized or aligned properly, they'd get an error telling them that the value they're trying to use is not good and suggesting a rounded up alternative. This way the size seen in the guest XML will reflect the one used at runtime, which is much less confusing than the existin behavior, and also the user will be able to create the backing file for the NVDIMM to be the exact size it needs to be instead of oversizing it. If we can't get this to work without impacting existing guests, then at the very least we should try to reflect the rounded down size in the inactive guest XML instead of waiting for guest startup. This is not as nice as the alternative, because it requires the user to actively seek the adjuste value, but still better than what we have right now. -- Andrea Bolognani / Red Hat / Virtualization
