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

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Wed, Mar 7, 2012 at 5:59 PM, George Dunlap
<george.dunlap@xxxxxxxxxxxxx> wrote:
> This is for a particular system we found with this problem; a HP DL785 with 
> BIOS
> dated 08/22/2008.
>
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

Hmm, actually, looking at our ticket (CA-24173, for those who have
access to it), I'm not sure this was ever actually shown to fix the
bug.  Tim, can you comment?

 -George

>
> diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
> --- 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;
> +        }
>         return -EINVAL;
>     }
>
> diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
> --- a/xen/include/asm-x86/msr-index.h
> +++ b/xen/include/asm-x86/msr-index.h
> @@ -198,6 +198,8 @@
>  /* MSR_K8_VM_CR bits: */
>  #define _K8_VMCR_SVME_DISABLE          4
>  #define K8_VMCR_SVME_DISABLE           (1 << _K8_VMCR_SVME_DISABLE)
> +#define _K8_VMCR_SVME_LOCK             3
> +#define K8_VMCR_SVME_LOCK              (1 << _K8_VMCR_SVME_LOCK)
>
>  /* AMD64 MSRs */
>  #define MSR_AMD64_NB_CFG               0xc001001f
>
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> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel

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