linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jan Beulich <JBeulich@suse.com>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	"olaf@aepfle.de" <olaf@aepfle.de>, "bp@alien8.de" <bp@alien8.de>,
	"apw@canonical.com" <apw@canonical.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"jasowang@redhat.com" <jasowang@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V
Date: Fri, 1 Feb 2013 13:19:37 +0000	[thread overview]
Message-ID: <alpine.DEB.2.02.1302011307440.10432@kaball.uk.xensource.com> (raw)
In-Reply-To: <510AE4F6.1050407@zytor.com>

On Thu, 31 Jan 2013, H. Peter Anvin wrote:
> On 01/30/2013 12:53 AM, Jan Beulich wrote:
> > 
> > I'm not convinced that's the right approach - any hypervisor
> > could do similar emulation, and hence you either want to make
> > sure you run on Hyper-V (by excluding all others), or you
> > tolerate using the emulation (which may require syncing up with
> > the other guest implementations so that shared resources don't
> > get used by two parties).
> > 
> > I also wonder whether using the Hyper-V emulation (where
> > useful, there might not be anything right now, but this may
> > change going forward) when no Xen support is configured
> > wouldn't be better than not using anything...
> > 
> 
> I'm confused about "the right approach" here is.  As far as I
> understand, this only can affect a Xen guest where HyperV guest support
> is enabled but not Xen support, and only because Xen emulates HyperV but
> does so incorrectly.
> 
> This is a Xen bug, and as such it makes sense to reject Xen
> specifically.  If another hypervisor emulates HyperV and does so
> correctly there seems to be no reason to reject it.

I don't think so.

AFAIK originally there were features exported as flags and Xen doesn't
turn on the flags that correspond to features that are not implemented.
The problem here is that Hyper-V is about to introduce a feature without
a flag that is not implemented by Xen (see "X86: Deliver Hyper-V
interrupts on a separate IDT vector").
K.Y. please confirm if I got this right.

If I were the Microsoft engineer implementing this feature, no matter
what Xen does or does not, I would also make sure that there is a
corresponding flag for it, because in my experience they avoid future
headaches.
I wonder what happens if you run Linux with Hyper-V support on an old
Hyper-V host that doesn't support vector injection.

  reply	other threads:[~2013-02-01 13:19 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-30  0:51 [PATCH 0/3] X86: Deliver Hyper-V interrupts on a seperate IDT vector K. Y. Srinivasan
2013-01-30  0:51 ` [PATCH 1/3] x86: Hyper-V: register clocksource only if its advertised K. Y. Srinivasan
2013-01-30  0:51   ` [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V K. Y. Srinivasan
2013-01-30  8:53     ` Jan Beulich
2013-01-30 18:12       ` KY Srinivasan
2013-01-30 18:19         ` H. Peter Anvin
2013-01-31  7:37         ` Jan Beulich
2013-01-31 14:46           ` KY Srinivasan
2013-01-31 15:53             ` KY Srinivasan
2013-01-31 16:45               ` Jan Beulich
2013-01-31 18:29                 ` H. Peter Anvin
2013-01-31 21:41       ` H. Peter Anvin
2013-02-01 13:19         ` Stefano Stabellini [this message]
2013-02-01 15:10           ` KY Srinivasan
2013-02-01 19:34             ` KY Srinivasan
2013-01-30  0:51   ` [PATCH 3/3] X86: Handle Hyper-V vmbus interrupts as special hypervisor interrupts K. Y. Srinivasan
2013-01-30  8:58     ` Jan Beulich
2013-01-31 14:55       ` KY Srinivasan
2013-02-04  1:21 [PATCH 0/3] X86: Deliver Hyper-V interrupts on a seperate IDT vector K. Y. Srinivasan
2013-02-04  1:22 ` [PATCH 1/3] x86: Hyper-V: register clocksource only if its advertised K. Y. Srinivasan
2013-02-04  1:22   ` [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V K. Y. Srinivasan
2013-04-17  7:06     ` Michael S. Tsirkin
2013-04-17 13:20       ` KY Srinivasan
2013-04-17 12:48         ` Michael S. Tsirkin
2013-04-17 14:12           ` KY Srinivasan
2013-04-17 13:25             ` Michael S. Tsirkin
2013-04-17 14:34               ` KY Srinivasan
2013-04-17 13:48                 ` Michael S. Tsirkin
2013-04-17 15:31                   ` KY Srinivasan
2013-04-17 15:50                     ` Jan Beulich
2013-04-17 16:28                       ` KY Srinivasan
2013-04-18  7:48                         ` Michael S. Tsirkin
2013-04-18 13:23                           ` KY Srinivasan
2013-04-18 13:30                             ` KY Srinivasan
2013-04-17 13:52         ` Jan Beulich
2013-04-17 13:01           ` Michael S. Tsirkin
2013-04-17 13:11             ` Michael S. Tsirkin
2013-04-17 14:09             ` Jan Beulich
2013-04-17 15:17               ` H. Peter Anvin

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=alpine.DEB.2.02.1302011307440.10432@kaball.uk.xensource.com \
    --to=stefano.stabellini@eu.citrix.com \
    --cc=JBeulich@suse.com \
    --cc=apw@canonical.com \
    --cc=bp@alien8.de \
    --cc=devel@linuxdriverproject.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=hpa@zytor.com \
    --cc=jasowang@redhat.com \
    --cc=kys@microsoft.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=olaf@aepfle.de \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    --subject='Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V' \
    /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

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).