netdev - Re: the XSK buffer pool needs be to reverted

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Date:   Fri, 26 Jun 2020 14:41:04 +0200
From:   Christoph Hellwig <hch@....de>
To:     Björn Töpel <bjorn.topel@...el.com>
Cc:     Christoph Hellwig <hch@....de>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        bpf <bpf@...r.kernel.org>,
        Maxim Mikityanskiy <maximmi@...lanox.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Björn Töpel <bjorn.topel@...il.com>
Subject: Re: the XSK buffer pool needs be to reverted

On Fri, Jun 26, 2020 at 02:22:41PM +0200, Björn Töpel wrote:
> Thanks for clarifying that. Let's work on a solution that can reside in
> the dma mapping core.
>
>> The commit seems to have a long dove tail of commits depending on it
>> despite only being a month old, so maybe you can do the revert for now?
>>
>
> Reverting the whole series sounds a bit too much. Let's focus on the
> part that breaks the dma api abstraction. I'm assuming that you're
> referring to the
>
>   static bool xp_check_cheap_dma(struct xsk_buff_pool *pool)
>
> function (and related functions called from that)?

Yes.

>
>> Note that this is somewhat urgent, as various of the APIs that the code
>> is abusing are slated to go away for Linux 5.9, so this addition comes
>> at a really bad time.
>>
>
> Understood. Wdyt about something in the lines of the diff below? It's
> build tested only, but removes all non-dma API usage ("poking
> internals"). Would that be a way forward, and then as a next step work
> on a solution that would give similar benefits, but something that would
> live in the dma mapping core?

Yes, that would solve the immediate issues.