[Qemu-devel] [PATCH] Fixed KVM problems with old DOS programs. Compatibility can be forced by module parameter.

[Gerhard Wiesinger <lists@wiesinger.com>]

Signed-off-by: Gerhard Wiesinger <lists@wiesinger.com>
---
  arch/x86/kvm/svm.c | 7 +++++++
  1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 2f9ed1f..e0b00fc 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -198,6 +198,10 @@ static bool npt_enabled;
  static int npt = true;
  module_param(npt, int, S_IRUGO);
  +/* allow backward compatibility with e.g. old DOS application */
+static int npt_task_switch_emulation = true;
+module_param(npt_task_switch_emulation, int, S_IRUGO);
+
  /* allow nested virtualization in KVM/SVM */
  static int nested = true;
  module_param(nested, int, S_IRUGO);
@@ -1177,6 +1181,9 @@ static void init_vmcb(struct vcpu_svm *svm, bool 
init_event)
  	if (npt_enabled) {
  		/* Setup VMCB for Nested Paging */
  		control->nested_ctl = 1;
+		if (!npt_task_switch_emulation) {
+			clr_intercept(svm, INTERCEPT_TASK_SWITCH);
+		}
  		clr_intercept(svm, INTERCEPT_INVLPG);
  		clr_exception_intercept(svm, PF_VECTOR);
  		clr_cr_intercept(svm, INTERCEPT_CR3_READ);
-- 
2.4.3