From: Christoph Hellwig <hch@lst.de>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: linux-s390@vger.kernel.org, Janosch Frank <frankja@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Cornelia Huck <cohuck@redhat.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Peter Oberparleiter <oberpar@linux.ibm.com>,
linux-kernel@vger.kernel.org,
Christian Borntraeger <borntraeger@de.ibm.com>,
iommu@lists.linux-foundation.org,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>,
Gerald Schaefer <gerald.schaefer@de.ibm.com>
Subject: Re: [RFC PATCH 1/3] dma-mapping: make overriding GFP_* flags arch customizable
Date: Fri, 27 Sep 2019 23:21:04 +0200 [thread overview]
Message-ID: <20190927212104.GC16819@lst.de> (raw)
In-Reply-To: <20190927023314.3e5c8324.pasic@linux.ibm.com>
On Fri, Sep 27, 2019 at 02:33:14AM +0200, Halil Pasic wrote:
> Thank you for your feedback. Just to be sure we are on the same pager, I
> read commit a0be1db4304f like this:
> 1) virtio_pci_legacy needs to allocate the virtqueues so that the base
> address fits 44 bits
> 2) if 64 bit dma is possible they set coherent_dma_mask to
> DMA_BIT_MASK(44) and dma_mask to DMA_BIT_MASK(64)
> 3) since the queues get allocated with coherent allocations 1) is
> satisfied
> 4) when the streaming mappings see a buffer that is beyond
> DMA_BIT_MASK(44) then it has to treat it as not coherent memory
> and do the syncing magic (which isn't actually required, just
> a side effect of the workaround.
1-3 is correct, 4 is not. The coherent mask is a little misnamed and
doesn't have to anything with coherency. It is the mask for DMA
allocations, while the dma mask is for streaming mappings.
> I've already implemented a patch (see after the scissors line) that
> takes a similar route as commit a0be1db4304f, but I consider that a
> workaround at best. But if that is what the community wants... I have to
> get the job done one way or the other.
That patch (minus the comments about being a workaround) is what you
should have done from the beginning.
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2019-09-27 21:21 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-23 12:34 [RFC PATCH 0/3] fix dma_mask for CCW devices Halil Pasic
2019-09-23 12:34 ` [RFC PATCH 1/3] dma-mapping: make overriding GFP_* flags arch customizable Halil Pasic
2019-09-23 15:21 ` Christoph Hellwig
2019-09-26 12:37 ` Halil Pasic
2019-09-26 13:04 ` Robin Murphy
2019-09-27 0:33 ` Halil Pasic
2019-09-27 21:21 ` Christoph Hellwig [this message]
2019-09-23 12:34 ` [RFC PATCH 2/3] s390/virtio: fix virtio-ccw DMA without PV Halil Pasic
2019-09-23 12:34 ` [RFC PATCH 3/3] dma-mapping: warn on harmful GFP_* flags Halil Pasic
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190927212104.GC16819@lst.de \
--to=hch@lst.de \
--cc=borntraeger@de.ibm.com \
--cc=cohuck@redhat.com \
--cc=frankja@linux.ibm.com \
--cc=gerald.schaefer@de.ibm.com \
--cc=gor@linux.ibm.com \
--cc=heiko.carstens@de.ibm.com \
--cc=iommu@lists.linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=oberpar@linux.ibm.com \
--cc=pasic@linux.ibm.com \
--cc=robin.murphy@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).