linux-kernel - Re: [PATCH RFC net-next 2/4] net: page_pool: avoid calling no-op externals when possible

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20230703133207.4f0c54ce@kernel.org>
Date:   Mon, 3 Jul 2023 13:32:07 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Alexander Duyck <alexanderduyck@...com>,
        "Jesper Dangaard Brouer" <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next 2/4] net: page_pool: avoid calling no-op
 externals when possible

On Fri, 30 Jun 2023 17:34:02 +0200 Alexander Lobakin wrote:
> > I am not a fan of having the page pool force the syncing either. Last
> > I knew I thought the PP_FLAG_DMA_SYNC_DEV was meant to be set by the  
> 
> Please follow the logics of the patch.
> 
> 1. The driver sets DMA_SYNC_DEV.
> 2. PP tries to shortcut and replaces it with MAYBE_SYNC.
> 3. If dma_need_sync() returns true for some page, it gets replaced back
>    to DMA_SYNC_DEV, no further dma_need_sync() calls for that pool.
> 
> OR
> 
> 1. The driver doesn't set DMA_SYNC_DEV.
> 2. PP doesn't turn on MAYBE_SYNC.
> 3. No dma_need_sync() tests.
> 
> Where does PP force syncs for drivers which don't need them?

I think both Alex and I got confused about what's going on here.

Could you reshuffle the code somehow to make it more obvious?
Rename the flag, perhaps put it in a different field than 
the driver-set PP flags?