CSTAR is an unused MSR in 64-bit mode on Intel's EM64T, hence there's no need
to save/restore this MSR during context switches. Mimic real hardware by
retaining the value written for eventual guest OS reads.
(Patch won't apply without the EFER adjustment patch.)
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Index: 2007-05-14/xen/arch/x86/hvm/vmx/vmx.c
===================================================================
--- 2007-05-14.orig/xen/arch/x86/hvm/vmx/vmx.c 2007-05-14 14:28:19.000000000
+0200
+++ 2007-05-14/xen/arch/x86/hvm/vmx/vmx.c 2007-05-14 14:33:24.000000000
+0200
@@ -88,8 +88,7 @@ static DEFINE_PER_CPU(struct vmx_msr_sta
static u32 msr_index[VMX_MSR_COUNT] =
{
- MSR_LSTAR, MSR_STAR, MSR_CSTAR,
- MSR_SYSCALL_MASK
+ MSR_LSTAR, MSR_STAR, MSR_SYSCALL_MASK
};
static void vmx_save_host_msrs(void)
@@ -147,7 +146,7 @@ static inline int long_mode_do_msr_read(
break;
case MSR_CSTAR:
- msr_content = guest_msr_state->msrs[VMX_INDEX_MSR_CSTAR];
+ msr_content = v->arch.hvm_vmx.cstar;
break;
case MSR_SYSCALL_MASK:
@@ -250,7 +249,8 @@ static inline int long_mode_do_msr_write
case MSR_CSTAR:
if ( !is_canonical_address(msr_content) )
goto uncanonical_address;
- WRITE_MSR(CSTAR);
+ v->arch.hvm_vmx.cstar = msr_content;
+ break;
case MSR_SYSCALL_MASK:
WRITE_MSR(SYSCALL_MASK);
@@ -730,12 +730,12 @@ static void vmx_save_cpu_state(struct vc
unsigned long guest_flags = guest_state->flags;
data->shadow_gs = v->arch.hvm_vmx.shadow_gs;
+ data->msr_cstar = v->arch.hvm_vmx.cstar;
/* save msrs */
data->msr_flags = guest_flags;
data->msr_lstar = guest_state->msrs[VMX_INDEX_MSR_LSTAR];
data->msr_star = guest_state->msrs[VMX_INDEX_MSR_STAR];
- data->msr_cstar = guest_state->msrs[VMX_INDEX_MSR_CSTAR];
data->msr_syscall_mask = guest_state->msrs[VMX_INDEX_MSR_SYSCALL_MASK];
#endif
@@ -755,9 +755,9 @@ static void vmx_load_cpu_state(struct vc
guest_state->flags = data->msr_flags;
guest_state->msrs[VMX_INDEX_MSR_LSTAR] = data->msr_lstar;
guest_state->msrs[VMX_INDEX_MSR_STAR] = data->msr_star;
- guest_state->msrs[VMX_INDEX_MSR_CSTAR] = data->msr_cstar;
guest_state->msrs[VMX_INDEX_MSR_SYSCALL_MASK] = data->msr_syscall_mask;
+ v->arch.hvm_vmx.cstar = data->msr_cstar;
v->arch.hvm_vmx.shadow_gs = data->shadow_gs;
#endif
Index: 2007-05-14/xen/include/asm-x86/hvm/vmx/vmcs.h
===================================================================
--- 2007-05-14.orig/xen/include/asm-x86/hvm/vmx/vmcs.h 2007-05-14
14:28:19.000000000 +0200
+++ 2007-05-14/xen/include/asm-x86/hvm/vmx/vmcs.h 2007-05-14
14:33:24.000000000 +0200
@@ -37,7 +37,6 @@ struct vmcs_struct {
enum {
VMX_INDEX_MSR_LSTAR = 0,
VMX_INDEX_MSR_STAR,
- VMX_INDEX_MSR_CSTAR,
VMX_INDEX_MSR_SYSCALL_MASK,
VMX_MSR_COUNT
@@ -77,6 +76,7 @@ struct arch_vmx_struct {
#ifdef __x86_64__
struct vmx_msr_state msr_state;
unsigned long shadow_gs;
+ unsigned long cstar;
#endif
unsigned long efer;
unsigned long vmxassist_enabled:1;
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