From: Kevin Wolf <kwolf@redhat.com>
To: Pavel Dovgalyuk <Pavel.Dovgaluk@gmail.com>
Cc: vsementsov@virtuozzo.com, qemu-devel@nongnu.org,
mreitz@redhat.com, dovgaluk@ispras.ru, pavel.dovgaluk@ispras.ru,
jsnow@redhat.com
Subject: Re: [PATCH v4] icount: make dma reads deterministic
Date: Wed, 3 Jun 2020 15:53:07 +0200 [thread overview]
Message-ID: <20200603135307.GD5127@linux.fritz.box> (raw)
In-Reply-To: <159117972206.12193.12939621311413561779.stgit@pasha-ThinkPad-X280>
Am 03.06.2020 um 12:22 hat Pavel Dovgalyuk geschrieben:
> From: Pavel Dovgalyuk <pavel.dovgaluk@gmail.com>
>
> Windows guest sometimes makes DMA requests with overlapping
> target addresses. This leads to the following structure of iov for
> the block driver:
>
> addr size1
> addr size2
> addr size3
>
> It means that three adjacent disk blocks should be read into the same
> memory buffer. Windows does not expects anything from these bytes
> (should it be data from the first block, or the last one, or some mix),
> but uses them somehow. It leads to non-determinism of the guest execution,
> because block driver does not preserve any order of reading.
>
> This situation was discusses in the mailing list at least twice:
> https://lists.gnu.org/archive/html/qemu-devel/2010-09/msg01996.html
> https://lists.gnu.org/archive/html/qemu-devel/2020-02/msg05185.html
>
> This patch makes such disk reads deterministic in icount mode.
> It splits the whole request into several parts. Parts may overlap,
> but SGs inside one part do not overlap.
> Parts that are processed later overwrite the prior ones in case
> of overlapping.
>
> Examples for different SG part sequences:
>
> 1)
> A1 1000
> A2 1000
> A1 1000
> A3 1000
> ->
> One request is split into two.
> A1 1000
> A2 1000
> --
> A1 1000
> A3 1000
>
> 2)
> A1 800
> A2 1000
> A1 1000
> ->
> A1 800
> A2 1000
> --
> A1 1000
>
> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Thanks, applied to the block branch.
Kevin
prev parent reply other threads:[~2020-06-03 13:54 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-03 10:22 [PATCH v4] icount: make dma reads deterministic Pavel Dovgalyuk
2020-06-03 13:53 ` Kevin Wolf [this message]
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=20200603135307.GD5127@linux.fritz.box \
--to=kwolf@redhat.com \
--cc=Pavel.Dovgaluk@gmail.com \
--cc=dovgaluk@ispras.ru \
--cc=jsnow@redhat.com \
--cc=mreitz@redhat.com \
--cc=pavel.dovgaluk@ispras.ru \
--cc=qemu-devel@nongnu.org \
--cc=vsementsov@virtuozzo.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).