From: Marcelo Tosatti <mtosatti@redhat.com>
To: Andre Przywara <andre.przywara@amd.com>
Cc: Avi Kivity <avi@redhat.com>,
Anthony Liguori <anthony@codemonkey.ws>,
KVM list <kvm@vger.kernel.org>, Alexander Graf <agraf@suse.de>
Subject: Re: unconditional CPUID propagation?
Date: Thu, 4 Aug 2011 11:07:29 -0300 [thread overview]
Message-ID: <20110804140729.GA16312@amt.cnet> (raw)
In-Reply-To: <4E3917D6.6030905@amd.com>
On Wed, Aug 03, 2011 at 11:41:42AM +0200, Andre Przywara wrote:
> 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.
Or if the CPU type supports it, yes.
prev parent reply other threads:[~2011-08-04 14:10 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-03 9:41 unconditional CPUID propagation? Andre Przywara
2011-08-04 14:07 ` Marcelo Tosatti [this message]
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