From: Jan Sacha <Jan.Sacha@alcatel-lucent.com>
To: <kvm@vger.kernel.org>
Subject: Re: IOTLB page size question
Date: Fri, 17 Oct 2014 14:01:14 -0700 [thread overview]
Message-ID: <5441839A.4030904@alcatel-lucent.com> (raw)
In-Reply-To: <543C5D34.4020406@alcatel-lucent.com>
On 10/13/2014 04:16 PM, Jan Sacha wrote:
>> Legacy KVM device assignment maps IOMMU pages using the host kernel page
>> size for the region while VFIO will pass the largest contiguous range of
>> pages available to the IOMMU, regardless of kernel page size. If VFIO
>> doesn't have the same problem then perhaps the kernel idea of the page
>> size for that reason has changed between mappings. Thanks,
> When I have a VM running, I can see on the host OS:
>
> # cat /proc/1360/numa_maps
> 2aaaaac00000 prefer:0
> file=/dev/hugepages/libvirt/qemu/qemu_back_mem.DO2GNu\040(deleted)
> huge dirty=3070 N0=3070
> ...
>
> # cat /proc/1360/maps
> 2aaaaac00000-2aac2a800000 rw-s 00000000 00:1e 19928
> /dev/hugepages/libvirt/qemu/qemu_back_mem.DO2GNu (deleted)
> ...
>
> So it looks to me that there should be roughly 6GB mapped using huge
> (2M) pages. PID 1360 is the qemu process. The VM is configured to use
> 6GB. However, the IOTLB seems to be using 2k pages for all memory
> below 4GB in the guest physical space. It does use 2M pages for memory
> above 4GB. Does this make sense?
We found a solution so I can answer my own question. This behavior was
caused by a bug in the kernel. It was fixed in 3.13.
https://github.com/torvalds/linux/commit/e0230e1327fb862c9b6cde24ae62d55f9db62c9b
Jan
prev parent reply other threads:[~2014-10-17 21:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-13 20:50 IOTLB page size question Jan Sacha
2014-10-13 21:41 ` Alex Williamson
2014-10-13 23:16 ` Jan Sacha
2014-10-17 21:01 ` Jan Sacha [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=5441839A.4030904@alcatel-lucent.com \
--to=jan.sacha@alcatel-lucent.com \
--cc=kvm@vger.kernel.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 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).