Re: [Xen-devel] [PATCH] xen: Try to work around a BIOS that disables SVM but does not lock it

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.03.12 at 18:59, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/svm/svm.c
> +++ b/xen/arch/x86/hvm/svm/svm.c
> @@ -1145,7 +1145,18 @@ static int svm_cpu_up(void)
>      rdmsrl(MSR_K8_VM_CR, msr_content);
>      if ( msr_content & K8_VMCR_SVME_DISABLE )
>      {
> -        printk("CPU%d: AMD SVM Extension is disabled in BIOS.\n", cpu);
> +        /* Try to re-enable it if we're allowed */
> +        if ( !(msr_content & K8_VMCR_SVME_LOCK) )
> +        {
> +            msr_content &= ~K8_VMCR_SVME_DISABLE;
> +            wrmsrl(MSR_K8_VM_CR, msr_content);
> +            rdmsrl(MSR_K8_VM_CR, msr_content);
> +        }
> +        if ( msr_content & K8_VMCR_SVME_DISABLE )
> +        {
> +            printk("AMD SVM Extension is disabled in BIOS.\n");
> +            return 0;

Returning success when you weren't able to enable SVM?

> +        }
>          return -EINVAL;

And failure when it worked?

>      }
>  

Also, shouldn't overriding of a BIOS setting be gated by a default-off
command line option?

Jan


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