From: Paolo Bonzini <pbonzini@redhat.com>
To: Stefan Bader <stefan.bader@canonical.com>
Cc: Jan Beulich <JBeulich@suse.com>,
"Justin M. Forbes" <jmforbes@linuxtx.org>,
Matt Wilson <msw@amazon.com>,
xen-devel@lists.xen.org,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [Xen-devel] [PATCH/RFC] Fix xsave bug on older Xen hypervisors
Date: Sat, 08 Sep 2012 12:20:16 +0200 [thread overview]
Message-ID: <504B1BE0.9040901@redhat.com> (raw)
In-Reply-To: <504A172B.5020005@canonical.com>
Il 07/09/2012 17:47, Stefan Bader ha scritto:
>
> Legacy hypervisors (RHEL 5.0 and RHEL 5.1) do not handle guest writes to
> cr4 gracefully. If a guest attempts to write a bit of cr4 that is
> unsupported, then the HV is so offended it crashes the domain. While
> later guest kernels (such as RHEL6) don't assume the HV supports all
> features, they do expect nicer responses. That assumption introduced
> code that probes whether or not xsave is supported early in the boot. So
> now when attempting to boot a RHEL6 guest on RHEL5.0 or RHEL5.1 an early
> crash will occur.
>
> This patch is quite obviously an undesirable hack. The real fix for this
> problem should be in the HV, and is, in later HVs. However, to support
> running on old HVs, RHEL6 can take this small change. No impact will
> occur for running on any RHEL HV (not even RHEL 5.5 supports xsave).
> There is only potential for guest performance loss on upstream Xen.
>
> All this by way of explanation for why is this patch not going upstream.
If it is just 5.0 and 5.1, you can restrict the patch to Xen 3.0.
5.2 switched to Xen 3.1, which has been subsequently patched to death
without rebasing.
Paolo
next prev parent reply other threads:[~2012-09-08 10:20 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-07 11:40 [PATCH/RFC] Fix xsave bug on older Xen hypervisors Stefan Bader
2012-09-07 12:33 ` [Xen-devel] " Jan Beulich
2012-09-07 13:21 ` Stefan Bader
2012-09-07 14:02 ` Jan Beulich
2012-09-07 14:22 ` Justin M. Forbes
2012-09-07 14:54 ` Konrad Rzeszutek Wilk
2012-09-08 10:18 ` Paolo Bonzini
2012-09-10 22:36 ` Matt Wilson
2012-09-07 15:44 ` Jan Beulich
2012-09-07 15:47 ` Stefan Bader
2012-09-07 15:52 ` Jan Beulich
2012-09-07 15:48 ` Konrad Rzeszutek Wilk
2012-09-07 16:13 ` Stefan Bader
2012-09-08 10:28 ` Paolo Bonzini
2012-09-07 15:54 ` Ian Campbell
2012-09-08 10:20 ` Paolo Bonzini [this message]
2012-09-07 16:00 ` Justin M. Forbes
2012-09-11 2:40 ` Matt Wilson
2012-09-11 11:37 ` Konrad Rzeszutek Wilk
2012-09-11 13:06 ` Josh Boyer
2012-09-07 13:47 ` Konrad Rzeszutek Wilk
2012-09-11 1:17 ` Matt Wilson
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=504B1BE0.9040901@redhat.com \
--to=pbonzini@redhat.com \
--cc=JBeulich@suse.com \
--cc=jmforbes@linuxtx.org \
--cc=konrad.wilk@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=msw@amazon.com \
--cc=stefan.bader@canonical.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 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).