Re: [PATCH] KVM: VMX: Inform user about INTEL_TXT dependency

[Avi Kivity <avi@redhat.com>]

On 11/14/2010 12:41 PM, Jan Kiszka wrote:
> Am 14.11.2010 11:30, Avi Kivity wrote:
> >  On 11/14/2010 11:18 AM, Jan Kiszka wrote:
> >>  From: Jan Kiszka<jan.kiszka@siemens.com>
> >>
> >>  Without CONFIG_INTEL_TXT, the user must not enable this feature in the
> >>  BIOS. Otherwise, KVM will not work. Explain this dependency via a kernel
> >>  log message.
> >>
> >>  Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
> >>  ---
> >>    arch/x86/kvm/vmx.c |    7 ++++++-
> >>    1 files changed, 6 insertions(+), 1 deletions(-)
> >>
> >>  diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> >>  index 9367abc..ebafd57 100644
> >>  --- a/arch/x86/kvm/vmx.c
> >>  +++ b/arch/x86/kvm/vmx.c
> >>  @@ -1306,8 +1306,13 @@ static __init int vmx_disabled_by_bios(void)
> >>                &&   tboot_enabled())
> >>                return 1;
> >>            if (!(msr&   FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX)
> >>  -&&   !tboot_enabled())
> >>  +&&   !tboot_enabled()) {
> >>  +#ifndef CONFIG_INTEL_TXT
> >>  +            printk(KERN_INFO "kvm: if TXT is enabled in the bios, "
> >>  +                     "kvm depends on CONFIG_INTEL_TXT\n");
> >>  +#endif
> >>                return 1;
> >>  +        }
> >>        }
> >>
> >
> >  Maybe reword to an instruction?
> >
> >  Something like
> >
> >    kvm: TXT enabled in the bios.  Either disable TXT in the bios, or
> >  enable CONFIG_INTEL_TXT in your kernel.
> >
>
> I always get an aching head when thinking about these dependency: Does
> FEATURE_CONTROL_LOCKED&&  !FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX
> imply that the BIOS uses TXT? Or could it also mean that it just
> disabled VT-x explicitly?

Probably the latter, at least that's what we took it to mean before it 
was renamed to that long string.

> As CONFIG_INTEL_TXT is off, we do not know if
> tboot_enabled is off as well.

I guess, if FEATURE_CONTROL_VMXON_ENABLED_INSIDER_SMX_YADA_YADA_YADA is 
set, then the bios wants us to enable TXT.  But if both bits are clear, 
the bios really doesn't want us to play with vmx.  But it would be good 
to get Intel guidance before we pass our confusion on to users.

-- 
error compiling committee.c: too many arguments to function