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[Xen-devel] Ping: [PATCH v3 1/8] x86/vmx_update_guest_cr: minor optimization



On 7/6/2016 6:49 PM, Corneliu ZUZU wrote:
Minor optimization @ vmx_update_guest_cr: checks if v->arch.hvm_vmx.exec_control
was modified before actually calling vmx_update_cpu_exec_control(v).

Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>
---
Changed since v2: <nothing>
---
  xen/arch/x86/hvm/vmx/vmx.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index df19579..8ab074f 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1434,8 +1434,10 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned 
int cr)
          if ( paging_mode_hap(v->domain) )
          {
              /* Manage GUEST_CR3 when CR0.PE=0. */
+            uint32_t old_ctls = v->arch.hvm_vmx.exec_control;
              uint32_t cr3_ctls = (CPU_BASED_CR3_LOAD_EXITING |
                                   CPU_BASED_CR3_STORE_EXITING);
+
              v->arch.hvm_vmx.exec_control &= ~cr3_ctls;
              if ( !hvm_paging_enabled(v) && !vmx_unrestricted_guest(v) )
                  v->arch.hvm_vmx.exec_control |= cr3_ctls;
@@ -1445,7 +1447,8 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned 
int cr)
                   monitor_ctrlreg_bitmask(VM_EVENT_X86_CR3) )
                  v->arch.hvm_vmx.exec_control |= CPU_BASED_CR3_LOAD_EXITING;
- vmx_update_cpu_exec_control(v);
+            if ( old_ctls != v->arch.hvm_vmx.exec_control )
+                vmx_update_cpu_exec_control(v);
          }
if ( !nestedhvm_vcpu_in_guestmode(v) )



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