# HG changeset patch
# User Keir Fraser <keir@xen.org>
# Date 1291116848 0
# Node ID 8420b82c22c2cad54860ffdbe8bcec21c65c86be
# Parent  d281061e6ec06bbbf8e2b0fadbeb9d1a04bc32e2
x86 hvm: Do not overwrite boot-cpu capability data on VMX/SVM startup.

Apparently required back in the earliest days of Xen, we now properly
initialise CPU capabilities early during bootstrap. Re-writing
capability data later now causes problems if specific features have
been deliberately masked out.

Thanks to Weidong Han at Intel for finding such a bug where XSAVE
feature is masked out by default, but then erroneously written back
during VMX initialisation. This would cause memory corruption problems
during boot for XSAVE-capable systems.

Signed-off-by: Keir Fraser <keir@xen.org>

--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -915,9 +915,6 @@ void start_svm(struct cpuinfo_x86 *c)
         return;
     }
 
-    /* Xen does not fill x86_capability words except 0. */
-    boot_cpu_data.x86_capability[5] = cpuid_ecx(0x80000001);
-
     if ( !test_bit(X86_FEATURE_SVME, &boot_cpu_data.x86_capability) )
         return;
 
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1433,9 +1433,6 @@ void start_vmx(void)
         return;
     }
 
-    /* Xen does not fill x86_capability words except 0. */
-    boot_cpu_data.x86_capability[4] = cpuid_ecx(1);
-
     if ( !test_bit(X86_FEATURE_VMXE, &boot_cpu_data.x86_capability) )
         return;