[PATCH v2 1/7] x86/vmx_update_guest_cr: minor optimization

From: Corneliu ZUZU <czuzu@bitdefender.com>
To: xen-devel@lists.xen.org
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Jan Beulich <jbeulich@suse.com>,
	Jun Nakajima <jun.nakajima@intel.com>
Subject: [PATCH v2 1/7] x86/vmx_update_guest_cr: minor optimization
Date: Tue,  5 Jul 2016 17:26:34 +0300	[thread overview]
Message-ID: <1467728794-13638-1-git-send-email-czuzu@bitdefender.com> (raw)
In-Reply-To: <1467728717-13592-1-git-send-email-czuzu@bitdefender.com>

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@bitdefender.com>
---
Changed since v1: <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) )
-- 
2.5.0


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