All of lore.kernel.org
 help / color / mirror / Atom feed
From: Juergen Gross <jgross@suse.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Michael Labriola <michael.d.labriola@gmail.com>,
	xen-devel@lists.xen.org, Paul Durrant <Paul.Durrant@citrix.com>,
	Jan Beulich <JBeulich@suse.com>
Subject: Re: Upstream Dom0 DRM problems regarding swiotlb
Date: Fri, 15 Feb 2019 06:57:27 +0100	[thread overview]
Message-ID: <f43c8fbf-8b6a-4bfc-8600-aba5f91e12ff@suse.com> (raw)
In-Reply-To: <20190214175705.GA21892@infradead.org>

On 14/02/2019 18:57, Christoph Hellwig wrote:
> On Thu, Feb 14, 2019 at 07:03:38AM +0100, Juergen Gross wrote:
>>> The thing which is different between Xen PV guests and most others (all
>>> others(?), now that Lguest and UML have been dropped) is that what Linux
>>> thinks of as PFN $N isn't necessarily adjacent to PFN $N+1 in system
>>> physical address space.
>>>
>>> Therefore, code which has a buffer spanning a page boundary can't just
>>> convert a pointer to the buffer into a physical address, and hand that
>>> address to a device.  You generally end up with either memory corruption
>>> (DMA hitting the wrong page allocated to the guest), or an IOMMU fault
>>> (DMA hitting a pages which isn't allocated to the guest).
> 
> The Linux DMA API allows for dma_map_page / dma_map_single calls to
> spawn 4k boundaries.  If Xen doesn't support that it will have to bounce
> buffer for that case (and get horrible performance).
> 
> But the latter text seems to agree with that.  So what is the actual
> problem that started this discussion?
> 

See https://lists.xen.org/archives/html/xen-devel/2019-02/threads.html#00818


Juergen

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

  reply	other threads:[~2019-02-15  5:57 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-12 18:46 Upstream Dom0 DRM problems regarding swiotlb Michael Labriola
2019-02-13 10:34 ` Jan Beulich
2019-02-13 14:10   ` Michael Labriola
2019-02-13 14:28     ` Jan Beulich
2019-02-13 16:00       ` Michael Labriola
2019-02-13 16:09         ` Jan Beulich
2019-02-13 16:56           ` Konrad Rzeszutek Wilk
2019-02-13 18:16             ` Michael Labriola
2019-02-13 18:38               ` Michael Labriola
2019-02-13 19:16                 ` Konrad Rzeszutek Wilk
2019-02-13 20:15                   ` Michael Labriola
2019-02-13 20:21                     ` Andrew Cooper
2019-02-13 21:08                       ` Michael Labriola
2019-02-14  0:11                         ` Andrew Cooper
2019-02-14  6:03                           ` Juergen Gross
2019-02-14 17:57                             ` Christoph Hellwig
2019-02-15  5:57                               ` Juergen Gross [this message]
2019-02-15 16:07                                 ` Michael Labriola
2019-02-15 16:26                                   ` Konrad Rzeszutek Wilk
2019-02-15 16:26                                   ` [Xen-devel] " Konrad Rzeszutek Wilk via dri-devel
2019-02-15 16:42                                   ` Christoph Hellwig
2019-02-14  6:01                 ` Juergen Gross
2019-02-14  8:03             ` Jan Beulich
2019-02-13 17:45           ` Michael Labriola
2019-02-14  8:05             ` Jan Beulich

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=f43c8fbf-8b6a-4bfc-8600-aba5f91e12ff@suse.com \
    --to=jgross@suse.com \
    --cc=JBeulich@suse.com \
    --cc=Paul.Durrant@citrix.com \
    --cc=andrew.cooper3@citrix.com \
    --cc=hch@infradead.org \
    --cc=konrad.wilk@oracle.com \
    --cc=michael.d.labriola@gmail.com \
    --cc=xen-devel@lists.xen.org \
    /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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.