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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

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>

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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