Re: [Xen-devel] [PATCH 01/16] x86/vmx_update_guest_cr: minor optimization

[Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>]

This was 1/8 in the old v3-series "x86/vm-event: Adjustments & fixes".
Transferring code-review from "Tian, Kevin <kevin.tian@xxxxxxxxx>" (July 11, 2016).

On 7/9/2016 7:12 AM, 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>
---
 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 0776d12..0798245 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1433,8 +1433,10 @@ 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;
@@ -1444,7 +1446,8 @@ 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) )

[Kevin wrote]:

    Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

---

Thanks,
Zuzu C.

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