linux-kernel - Re: [PATCH] virtio_ring: skip cpu sync when mapping fails

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: <20241112164527-mutt-send-email-mst@kernel.org>
Date: Tue, 12 Nov 2024 16:45:51 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: xuanzhuo@...ux.alibaba.com, eperezma@...hat.com,
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_ring: skip cpu sync when mapping fails

On Mon, Nov 11, 2024 at 04:36:52PM +0800, Jason Wang wrote:
> On Mon, Nov 11, 2024 at 3:30 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > On Mon, Nov 11, 2024 at 10:55:38AM +0800, Jason Wang wrote:
> > > There's no need to sync DMA for CPU on mapping errors. So this patch
> > > skips the CPU sync in the error handling path of DMA mapping.
> > >
> > > Signed-off-by: Jason Wang <jasowang@...hat.com>
> >
> > DMA sync is idempotent.
> > Extra work for slow path.  Why do we bother?
> 
> dma_map_sg() did this, since current virtio hack sg mappings to per
> page mapping, we lose such optimization.
> 
> Actually the path is not necessarily slowpath in some setups like
> swiotlb or VDUSE.
> 
> Thanks

I don't get how it's not a slowpath. Example?

-- 
MST