public inbox for kvm@vger.kernel.org
 help / color / mirror / Atom feed
From: Andre Przywara <andre.przywara@amd.com>
To: Avi Kivity <avi@redhat.com>, Anthony Liguori <anthony@codemonkey.ws>
Cc: KVM list <kvm@vger.kernel.org>, Alexander Graf <agraf@suse.de>
Subject: unconditional CPUID propagation?
Date: Wed, 3 Aug 2011 11:41:42 +0200	[thread overview]
Message-ID: <4E3917D6.6030905@amd.com> (raw)

Hi,

while looking through the code I found commit
f79116867ec80ed5d1d10043a3fd9ac8afd182c1 (upstream QEMU: enable SMEP) 
which unconditionally propagates the bits from CPUID leaf 0x7 to the 
guest. Though there is the KVM module in the line, this currently 
whitelists three feature bits.
Doesn't that break migration? The result of the CPUID instruction the 
guess issues only depends on the host and the KVM module's policy, not 
on the CPU model QEMU uses. So I guess migrating from a newer CPU to an 
older one breaks despite a rather conservative CPU model has been chosen 
intentionally by the user.
The same is probably true for the VIA CPUID leaf.

Is that considered OK now or is that a bug? Shall the new feature bits 
be made known to QEMU like the other ones on only enabled explicitly 
(+smep) or by -cpu host?
I can make a patch for that if that is the right way to address this.

Regards,
Andre.

-- 
Andre Przywara
AMD-OSRC (Dresden)
Tel: x29712



             reply	other threads:[~2011-08-03  9:45 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-08-03  9:41 Andre Przywara [this message]
2011-08-04 14:07 ` unconditional CPUID propagation? Marcelo Tosatti

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=4E3917D6.6030905@amd.com \
    --to=andre.przywara@amd.com \
    --cc=agraf@suse.de \
    --cc=anthony@codemonkey.ws \
    --cc=avi@redhat.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