From: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx> Sent: Friday, May 22, 2020 9:40 AM > > > > + if (hv_do_hypercall(HV_EXT_CALL_QUERY_CAPABILITIES, NULL, cap) == > > > + HV_STATUS_SUCCESS) > > > > You're using the input page as the output parameter. Ideally we should > > introduce hyperv_pcpu_output_arg page, but that would waste one page per > > cpu just for this one call. > > > > So for now I think this setup is fine, but I would like to add the > > following comment. > > > > /* > > * Repurpose the input_arg page to accept output from Hyper-V for > > * now because this is the only call that needs output from the > > * hypervisor. It should be fixed properly by introducing an > > * output_arg page once we have more places that require output. > > */ > > Sounds good. Will add it in v2. > Note that the only real requirement for the output parameter to hypercalls is that it not cross a page boundary. Since '*cap' is only 64-bits, you can declare it as a static variable or even as a local on the stack. It will naturally be aligned (or can add __aligned(8) to be explicit??), so it won't cross a page boundary. Then you can skip using the per-cpu input arg altogether, along with the associated local_irq_save()/restore(). Michael
