linux-kernel - Re: [RFC] dma-mapping: introduce dma_can_skip

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]

Date: Fri, 1 Mar 2024 06:50:05 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Robin Murphy <robin.murphy@....com>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, linux-kernel@...r.kernel.org,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Christoph Hellwig <hch@....de>,
	Marek Szyprowski <m.szyprowski@...sung.com>, iommu@...ts.linux.dev,
	Zelin Deng <zelin.deng@...ux.alibaba.com>
Subject: Re: [RFC] dma-mapping: introduce dma_can_skip_unmap()

On Fri, Mar 01, 2024 at 11:38:25AM +0000, Robin Murphy wrote:
> Not only is this idea not viable, the entire premise seems flawed - the
> reasons for virtio needing to use the DMA API at all are highly likely to be
> the same reasons for it needing to use the DMA API *properly* anyway.

The idea has nothing to do with virtio per se - we are likely not the
only driver that wastes a lot of memory (hot in cache, too) keeping DMA
addresses around for the sole purpose of calling DMA unmap.  On a bunch
of systems unmap is always a nop and we could save some memory if there
was a way to find out. What is proposed is an API extension allowing
that for anyone - not just virtio.

-- 
MST