Hi Paolo, On Wed, 2 Oct 2024 at 10:38, Paolo Abeni <pabeni@xxxxxxxxxx> wrote: > > Hi, > > On 10/2/24 04:34, Yunsheng Lin wrote: > > On 10/1/2024 9:32 PM, Paolo Abeni wrote: > >> Is the problem only tied to VFs drivers? It's a pity all the page_pool > >> users will have to pay a bill for it... > > > > I am afraid it is not only tied to VFs drivers, as: > > attempting DMA unmaps after the driver has already unbound may leak > > resources or at worst corrupt memory. > > > > Unloading PFs driver might cause the above problems too, I guess the > > probability of crashing is low for the PF as PF can not be disable > > unless it can be hot-unplug'ed, but the probability of leaking resources > > behind the dma mapping might be similar. > > Out of sheer ignorance, why/how the refcount acquired by the page pool > on the device does not prevent unloading? > > I fear the performance impact could be very high: AFICS, if the item > array become fragmented, insertion will take linar time, with the quite > large item_count/pool size. If so, it looks like a no-go. It would be could if someone could test that. I'll look around in case we have any test machines with cards that run on page pool. > > I fear we should consider blocking the device removal until all the > pages are returned/unmapped ?!? (I hope that could be easier/faster) Jakub send an RFC doing that [0]. Yes, this is far far simpler and does not affect performance, but aren't we implicitly breaking userspace? [0] https://lore.kernel.org/netdev/20240806151618.1373008-1-kuba@xxxxxxxxxx/ Thanks /Ilias > > /P >
