[Xen-changelog] [xen-unstable] x86 hvm: Do not overwrite boot-cpu capability data on VMX/SVM startup.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir@xxxxxxx>
# 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@xxxxxxx>
---
 xen/arch/x86/hvm/svm/svm.c |    3 ---
 xen/arch/x86/hvm/vmx/vmx.c |    3 ---
 2 files changed, 6 deletions(-)

diff -r d281061e6ec0 -r 8420b82c22c2 xen/arch/x86/hvm/svm/svm.c
--- a/xen/arch/x86/hvm/svm/svm.c        Mon Nov 29 17:44:32 2010 +0000
+++ b/xen/arch/x86/hvm/svm/svm.c        Tue Nov 30 11:34:08 2010 +0000
@@ -885,9 +885,6 @@ static int svm_cpu_up(void)
 
 struct hvm_function_table * __init start_svm(void)
 {
-    /* 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 NULL;
 
diff -r d281061e6ec0 -r 8420b82c22c2 xen/arch/x86/hvm/vmx/vmx.c
--- a/xen/arch/x86/hvm/vmx/vmx.c        Mon Nov 29 17:44:32 2010 +0000
+++ b/xen/arch/x86/hvm/vmx/vmx.c        Tue Nov 30 11:34:08 2010 +0000
@@ -1394,9 +1394,6 @@ static struct hvm_function_table __read_
 
 struct hvm_function_table * __init start_vmx(void)
 {
-    /* 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 NULL;
 

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