Re: [Intel-wired-lan] [PATCH net-next] ice: access @pp through netmem_desc instead of page

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Pavel Begunkov <asml.silence@gmail.com>
Date: Wed, 17 Dec 2025 13:11:28 +0000

> On 12/16/25 04:20, Matthew Wilcox wrote:
>> On Tue, Dec 16, 2025 at 01:07:23PM +0900, Byungchul Park wrote:
>>> +++ b/drivers/net/ethernet/intel/ice/ice_ethtool.c
>>> @@ -1251,7 +1251,7 @@ static int ice_lbtest_receive_frames(struct
>>> ice_rx_ring *rx_ring)
>>>           rx_buf = &rx_ring->rx_fqes[i];
>>>           page = __netmem_to_page(rx_buf->netmem);
>>>           received_buf = page_address(page) + rx_buf->offset +
>>> -                   page->pp->p.offset;
>>> +                   pp_page_to_nmdesc(page)->pp->p.offset;
>>
>> Shouldn't we rather use:
>>
>>         nmdesc = __netmem_to_nmdesc(rx_buf->netmem);
>>         received_buf = nmdesc_address(nmdesc) + rx_buf->offset +
>>                 nmdesc->pp->p_offset;
>>
>> (also. i think we're missing a nmdesc_address() function in our API).
> 
> It wouldn't make sense as net_iov backed nmdescs don't have/expose
> host addresses (only dma addresses). nmdesc_address() would still
> need to rely on the caller knowing that it's a page. An explicit
> cast with *netmem_to_page() should be better.

Sorry for the late reply. Holidays... Happy New Year everyone.

I agree with Pavel. This loopback test always operates with
kernel/page-backed memory. I believe it's fully valid to explicitly cast
to a page in such cases and work with it. This is also more clear to the
readers after all (IIRC I suggested this piece of code when Michał was
working on the ice conversion).

Thanks,
Olek