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



On 7/8/2016 2:48 PM, Jan Beulich wrote:
On 08.07.16 at 13:39, <czuzu@xxxxxxxxxxxxxxx> wrote:
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) )
I'm wondering if you could ack this as well (if there's nothing wrong w/
it) and push it to be done with it. :-)
Well, if you had pinged the patch at least once, I probably would.
I don't, however, recall having seen any such ping (only resends).

Jan

So is a 'ping' (haven't done that before) still necessary? Is a ping a simple 'reply-to-all' including 'Ping: ' in the subject? :-)

Thanks,
Corneliu.

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