Leendert van Doorn
2005-May-28 14:40 UTC
[Xen-devel] [PATCH] VMX world switch does not handle all cases
The latest world switch modification does not handle all cases. Specifically,
when a partition enables CR0.PG|CR0.PE and performs a world switch at the
the same time. The patch below handles this case.
Signed-Off-By: Leendert van Doorn <leendert@watson.ibm.com>
--- xeno-unstable.orig/xen/arch/x86/vmx.c 2005-05-28 10:29:32.000000000 -0400
+++ xeno-unstable.mine/xen/arch/x86/vmx.c 2005-05-28 10:39:59.000000000 -0400
@@ -744,8 +744,8 @@
__vmwrite(CR0_READ_SHADOW, value);
VMX_DBG_LOG(DBG_LEVEL_VMMU, "Update CR0 value = %lx\n", value);
- if ((value & X86_CR0_PE) && (value & X86_CR0_PG)
- && !paging_enabled) {
+
+ if ((value & X86_CR0_PE) && (value & X86_CR0_PG) &&
!paging_enabled) {
/*
* The guest CR3 must be pointing to the guest physical.
*/
@@ -775,33 +775,39 @@
*/
VMX_DBG_LOG(DBG_LEVEL_VMMU, "Update CR3 value = %lx, mfn =
%lx",
d->arch.arch_vmx.cpu_cr3, mfn);
- } else {
- if ((value & X86_CR0_PE) == 0) {
- __vmread(GUEST_EIP, &eip);
- VMX_DBG_LOG(DBG_LEVEL_1, "Disabling CR0.PE at %%eip
0x%lx\n", eip);
- if (vmx_assist(d, VMX_ASSIST_INVOKE)) {
- set_bit(VMX_CPU_STATE_ASSIST_ENABLED,
- &d->arch.arch_vmx.cpu_state);
- __vmread(GUEST_EIP, &eip);
- VMX_DBG_LOG(DBG_LEVEL_1,
- "Transfering control to vmxassist %%eip 0x%lx", eip);
- return 0; /* do not update eip! */
- }
- } else if (test_bit(VMX_CPU_STATE_ASSIST_ENABLED,
- &d->arch.arch_vmx.cpu_state)) {
+ }
+
+ /*
+ * VMX does not implement real-mode virtualization. We emulate
+ * real-mode by performing a world switch to VMXAssist whenever
+ * a partition disables the CR0.PE bit.
+ */
+ if ((value & X86_CR0_PE) == 0) {
+ __vmread(GUEST_EIP, &eip);
+ VMX_DBG_LOG(DBG_LEVEL_1,
+ "Disabling CR0.PE at %%eip 0x%lx\n", eip);
+ if (vmx_assist(d, VMX_ASSIST_INVOKE)) {
+ set_bit(VMX_CPU_STATE_ASSIST_ENABLED, &d->arch.arch_vmx.cpu_state);
__vmread(GUEST_EIP, &eip);
VMX_DBG_LOG(DBG_LEVEL_1,
- "Enabling CR0.PE at %%eip 0x%lx", eip);
- if (vmx_assist(d, VMX_ASSIST_RESTORE)) {
- clear_bit(VMX_CPU_STATE_ASSIST_ENABLED,
+ "Transfering control to vmxassist %%eip 0x%lx\n", eip);
+ return 0; /* do not update eip! */
+ }
+ } else if (test_bit(VMX_CPU_STATE_ASSIST_ENABLED,
+ &d->arch.arch_vmx.cpu_state)) {
+ __vmread(GUEST_EIP, &eip);
+ VMX_DBG_LOG(DBG_LEVEL_1,
+ "Enabling CR0.PE at %%eip 0x%lx\n", eip);
+ if (vmx_assist(d, VMX_ASSIST_RESTORE)) {
+ clear_bit(VMX_CPU_STATE_ASSIST_ENABLED,
&d->arch.arch_vmx.cpu_state);
- __vmread(GUEST_EIP, &eip);
- VMX_DBG_LOG(DBG_LEVEL_1,
- "Restoring to %%eip 0x%lx", eip);
- return 0; /* do not update eip! */
- }
+ __vmread(GUEST_EIP, &eip);
+ VMX_DBG_LOG(DBG_LEVEL_1,
+ "Restoring to %%eip 0x%lx\n", eip);
+ return 0; /* do not update eip! */
}
}
+
return 1;
}
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