From: Long Li <lon...@microsoft.com> Sent: Wednesday, April 23, 2025 11:49 AM > > > > > > Interrupt and monitor pages should be in Hyper-V page size (4k bytes). > > > This can be different to the system page size. > > > > I'm curious about this change. Since Patch 1 of the series changes the > > allocations > > to be the full PAGE_SIZE, what does it mean to set the mapping size to less > > than a > > full page (in the case PAGE_SIZE > HV_HYP_PAGE_SIZE)? mmap can only map full > > PAGE_SIZE pages, so uio_mmap() rounds up the INT_PAGE_MAP and > > MON_PAGE_MAP sizes to PAGE_SIZE when checking the validity of the mmap > > parameters. > > > > The changes in this patch do ensure that the INT_PAGE_MAP and > > MON_PAGE_MAP "maps" entries in sysfs always show the size as > > 4096 even if the full PAGE_SIZE is actually mapped, but I'm not sure if that > > difference is good or bad. > > Kernel needs to tell the user-mode the correct length of the map. In this > case, 4096 > bytes are usable data regardless of what is actual mapped as long as it's > >4096. > > The DPDK vmbus driver uses this length to setup checks for accessing the page.
OK, so the "maps" entry needs to show a size of 4096 so the DPDK VMBus driver does the right thing. At a minimum, mention in the commit message that the reason for the change is to always show 4096 as the size of the "maps" entries, even if PAGE_SIZE and the actual mapped area is larger. Perhaps also mention that the DPDK VMBus driver is one known consumer of that detail. Michael
