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Re: [Qemu-devel] Re: [PATCH 3/4] mask out forbidden cpuid features with


From: Avi Kivity
Subject: Re: [Qemu-devel] Re: [PATCH 3/4] mask out forbidden cpuid features with kvm ioctl
Date: Tue, 03 Feb 2009 23:25:47 +0200
User-agent: Thunderbird 2.0.0.19 (X11/20090105)

Anthony Liguori wrote:
Glauber Costa wrote:
KVM has a (so far unused) ioctl to inform userspace
about supported cpuid bits in the current host.

The lack of this kind of checking can lead to bugs in which
a cpuid bit is exposed but not supported by the host kernel
(an example is fedora bug https://bugzilla.redhat.com/show_bug.cgi?id=481274)

The current host_cpuid code is replaced by this general check.

Signed-off-by: Glauber Costa <address@hidden>

So what do we do about live migration?

We need a way to completely specify cpuid from the command line. The management utility would figure out what is supported (driven by both cpu capabilities and installed kvm capabilities) and fgure out a greatest common denominator, or something.

Does KVM mask a set of bits unconditionally?

The kernel doesn't touch cpuid (except nx due to an historical mistake).

Before, we were masking unconditionally which should insulate migration reasonable well.

That suits migration, but not other uses of qemu.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.





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