linux-kernel - Re: [x86] 5ac0c41bf3: WARNING: CPU: 0 PID: 0 at arch/x86/mm/extable.c:50 ex_handler_rdmsr

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Date:	Wed, 15 Jun 2016 19:07:43 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Eduardo Habkost <ehabkost@...hat.com>
Cc:	kernel test robot <fengguang.wu@...el.com>,
	Andy Lutomirski <luto@...capital.net>,
	Paolo Bonzini <pbonzini@...hat.com>, LKP <lkp@...org>,
	wfg@...ux.intel.com, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [x86] 5ac0c41bf3:  WARNING: CPU: 0 PID: 0 at
 arch/x86/mm/extable.c:50 ex_handler_rdmsr_unsafe

On Wed, Jun 15, 2016 at 11:51:50AM -0300, Eduardo Habkost wrote:
> We have that: it is "-feature" (or "feature=off"). Features that
> can't be configured in the command-line should never appear to
> the guest unless you use "-cpu host,migratable=off".
> 
> Something that allows disabling feature flags that still don't
> have a name in QEMU would be useful for "-cpu
> host,migratable=off" only (and that's an interesting suggestion).
> But that's not the case here, I guess.

Right, and I'm wondering whether something like that would be useful for
testing purposes. For example, I want to enable a CPUID feature on the
command line and see how the kernel I'm booting in the guest reacts. And
that feature bit is not necessarily known to qemu/kvm.

Can we, say, pass whole CPUID leafs to qemu to report to the guest?
I.e., something like:

 ... -cpuid=0x5,eax=0x40,ebx=0xdeadbeef,ecx=0xcaffee ...

and so on.

Would that be interesting to add to qemu? I'd find something like that
very useful for testing kernels...

Thanks.

-- 
Regards/Gruss,
    Boris.

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