Re: regression: nested: L1 3.15+ fails to load kvm-intel on L0 <3.15

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/03/2015 09:46, Stefan Bader wrote:
> 
> Regardless of that, I wonder whether the below (this version untested) sound
> acceptable for upstream? At least it would make debugging much simpler. :)
> 
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2953,8 +2953,11 @@ static __init int adjust_vmx_controls(u32 ctl_min, u32 ct
>         ctl |= vmx_msr_low;  /* bit == 1 in low word  ==> must be one  */
> 
>         /* Ensure minimum (required) set of control bits are supported. */
> -       if (ctl_min & ~ctl)
> +       if (ctl_min & ~ctl) {
> +               printk(KERN_ERR "vmx: msr(%08x) does not match requirements. "
> +                               "req=%08x cur=%08x\n", msr, ctl_min, ctl);
>                 return -EIO;
> +       }
> 
>         *result = ctl;
>         return 0;

Yes, this is nice.  Maybe -ENODEV.

Also, a minimal patch for Ubuntu would probably be:

@@ -2850,7 +2851,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
 		      vmx_capability.ept, vmx_capability.vpid);
 	}
 
-	min = 0;
+	min = VM_EXIT_SAVE_DEBUG_CONTROLS;
 #ifdef CONFIG_X86_64
 	min |= VM_EXIT_HOST_ADDR_SPACE_SIZE;
 #endif

but I don't think it's a good idea to add it to stable kernels.

Paolo