[Xen-devel] [PATCH 2/3] x86/vmx: Don't self-recurse in vmx_update_guest_cr()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

An update to CR4 following a CR0 update can be done easily by falling
through into the CR4 case.  This avoids unnecessary passes through
vmx_vmcs_{enter,exit}() and unnecessary stack usage (as the compiler
cannot optimise this use to a tailcall).

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
CC: Kevin Tian <kevin.tian@xxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmx.c | 40 ++++++++++++++++++----------------------
 1 file changed, 18 insertions(+), 22 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 61047e0..5b943d4 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1627,29 +1627,8 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned 
int cr)
         v->arch.hvm_vcpu.hw_cr[0] =
             v->arch.hvm_vcpu.guest_cr[0] | hw_cr0_mask;
         __vmwrite(GUEST_CR0, v->arch.hvm_vcpu.hw_cr[0]);
-
-        /* Changing CR0 can change some bits in real CR4. */
-        vmx_update_guest_cr(v, 4);
-        break;
     }
-
-    case 2:
-        /* CR2 is updated in exit stub. */
-        break;
-
-    case 3:
-        if ( paging_mode_hap(v->domain) )
-        {
-            if ( !hvm_paging_enabled(v) && !vmx_unrestricted_guest(v) )
-                v->arch.hvm_vcpu.hw_cr[3] =
-                    v->domain->arch.hvm_domain.params[HVM_PARAM_IDENT_PT];
-            vmx_load_pdptrs(v);
-        }
-
-        __vmwrite(GUEST_CR3, v->arch.hvm_vcpu.hw_cr[3]);
-        hvm_asid_flush_vcpu(v);
-        break;
-
+        /* Fallthrough: Changing CR0 can change some bits in real CR4. */
     case 4:
         v->arch.hvm_vcpu.hw_cr[4] = HVM_CR4_HOST_MASK;
         if ( paging_mode_hap(v->domain) )
@@ -1681,6 +1660,23 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned 
int cr)
         __vmwrite(GUEST_CR4, v->arch.hvm_vcpu.hw_cr[4]);
         break;
 
+    case 2:
+        /* CR2 is updated in exit stub. */
+        break;
+
+    case 3:
+        if ( paging_mode_hap(v->domain) )
+        {
+            if ( !hvm_paging_enabled(v) && !vmx_unrestricted_guest(v) )
+                v->arch.hvm_vcpu.hw_cr[3] =
+                    v->domain->arch.hvm_domain.params[HVM_PARAM_IDENT_PT];
+            vmx_load_pdptrs(v);
+        }
+
+        __vmwrite(GUEST_CR3, v->arch.hvm_vcpu.hw_cr[3]);
+        hvm_asid_flush_vcpu(v);
+        break;
+
     default:
         BUG();
     }
-- 
2.1.4


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