Xen devel - Mar 2012 - [PATCH] xen: Try to work around a BIOS that disables SVM but does not lock it

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@eu.citrix.com>

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

On Wed, Mar 7, 2012 at 5:59 PM, George Dunlap
<george.dunlap@eu.citrix.com> 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@eu.citrix.com>
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
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

>>> On 07.03.12 at 18:59, George Dunlap
<george.dunlap@eu.citrix.com> 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

At 18:04 +0000 on 07 Mar (1331143469), George Dunlap
wrote:
> On Wed, Mar 7, 2012 at 5:59 PM, George Dunlap
> <george.dunlap@eu.citrix.com> 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@eu.citrix.com>
> 
> 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?
I''m afraid I can''t remember any more than is on the ticket -
that was
more than two years ago. :) Do you still have one of these machines in
service to test it?

TBH, though, the ''disabled but not locked'' state is a BIOS bug
-
esp. since the ticket says that the BIOS claimed SVM was enabled.  
IIRC I put this patch in because we were very close to a product release
at the time and we couldn''t be sure that we wouldn''t hit this
problem on
a lot of other customer h/w.

Tim