Re: [PATCH net v2 2/2] page_pool: fix IOMMU crash when driver has already unbound

[Paolo Abeni]

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.

I fear we should consider blocking the device removal until all the 
pages are returned/unmapped ?!? (I hope that could be easier/faster)

/P