Re: [RFC] x86 Host CPU features detection by MSRs
On Wed, Jul 09, 2025 at 05:58:03AM -0400, Andrea Bolognani wrote:
On Wed, Jul 09, 2025 at 09:53:40AM +0100, Daniel P. Berrangé via
Devel wrote:
> On Wed, Jul 09, 2025 at 10:29:32AM +0200, Hector Cao wrote:
> > > > 3. if that fails too, load the msr module and try again;
> > >
> > > It seems like a modules-load file is simpler than having this manual
> > > kmod load + repeat.
Well, we can perform the load unconditionally too. I was concerned
that doing so would result in a failure on Fedora and other distros
that have msr built-in, but I just tried and it seems that modprobe
is smart enough to handle that scenario gracefully.
The other question is what to do if we can't read the msr
information. It seems that right now we report the incorrect CPU
model, which is obviously not ideal. Raising an error would probably
be better, but I'm not sure whether the APIs are really designed in a
way that makes that possible.
IMHO an inability to read the msr info is a distro integration bug.
Given the /dev/kvm fallback, the most common failure scenario will
be on distros where /dev/kvm is restricted access. At that point
though you can't run KVM enabled guests anyway, so the MSR problem
is the least of your worries, as the info obtanied from MSRs is
not especially relevant to TCG usage.
With regards,
Daniel
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