x86/vmx: Internal cleanup for MSR load/save infrastructure

* Use an arch_vmx_struct local variable to reduce later code volume.
 * Use start/total instead of msr_area/msr_count.  This is in preparation for
   more finegrained handling with later changes.
 * Use ent/end pointers (again for preparation), and to make the vmx_add_msr()
   logic easier to follow.
 * Make the memory allocation block of vmx_add_msr() unlikely, and calculate
   virt_to_maddr() just once.

No practical change to functionality.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
(cherry picked from commit 94fda356fc)

xen/arch/x86/hvm/vmx/vmcs.c

@@ -1315,33 +1315,33 @@ static int construct_vmcs(struct vcpu *v)
 struct vmx_msr_entry *vmx_find_msr(uint32_t msr, enum vmx_msr_list_type type)
 {
     struct vcpu *curr = current;
-    unsigned int msr_count;
-    struct vmx_msr_entry *msr_area = NULL;
-    unsigned int i;
+    struct arch_vmx_struct *vmx = &curr->arch.hvm_vmx;
+    struct vmx_msr_entry *start = NULL;
+    unsigned int i, total;
 
     switch ( type )
     {
     case VMX_MSR_HOST:
-        msr_count = curr->arch.hvm_vmx.host_msr_count;
-        msr_area = curr->arch.hvm_vmx.host_msr_area;
+        start    = vmx->host_msr_area;
+        total    = vmx->host_msr_count;
         break;
 
     case VMX_MSR_GUEST:
-        msr_count = curr->arch.hvm_vmx.msr_count;
-        msr_area = curr->arch.hvm_vmx.msr_area;
+        start    = vmx->msr_area;
+        total    = vmx->msr_count;
         break;
 
     default:
         ASSERT_UNREACHABLE();
     }
 
-    if ( msr_area == NULL )
+    if ( !start )
         return NULL;
 
-    for ( i = 0; i < msr_count; i++ )
+    for ( i = 0; i < total; i++ )
     {
-        if ( msr_area[i].index == msr )
-            return &msr_area[i];
+        if ( start[i].index == msr )
+            return &start[i];
     }
 
     return NULL;
@@ -1350,19 +1350,20 @@ struct vmx_msr_entry *vmx_find_msr(uint32_t msr, enum vmx_msr_list_type type)
 int vmx_add_msr(uint32_t msr, enum vmx_msr_list_type type)
 {
     struct vcpu *curr = current;
-    unsigned int idx, *msr_count;
-    struct vmx_msr_entry **msr_area, *msr_area_elem;
+    struct arch_vmx_struct *vmx = &curr->arch.hvm_vmx;
+    struct vmx_msr_entry **ptr, *start = NULL, *ent, *end;
+    unsigned int total;
 
     switch ( type )
     {
     case VMX_MSR_HOST:
-        msr_count = &curr->arch.hvm_vmx.host_msr_count;
-        msr_area = &curr->arch.hvm_vmx.host_msr_area;
+        ptr      = &vmx->host_msr_area;
+        total    = vmx->host_msr_count;
         break;
 
     case VMX_MSR_GUEST:
-        msr_count = &curr->arch.hvm_vmx.msr_count;
-        msr_area = &curr->arch.hvm_vmx.msr_area;
+        ptr      = &vmx->msr_area;
+        total    = vmx->msr_count;
         break;
 
     default:
@@ -1370,48 +1371,55 @@ int vmx_add_msr(uint32_t msr, enum vmx_msr_list_type type)
         return -EINVAL;
     }
 
-    if ( *msr_area == NULL )
+    /* Allocate memory on first use. */
+    if ( unlikely(!*ptr) )
     {
-        if ( (*msr_area = alloc_xenheap_page()) == NULL )
+        paddr_t addr;
+
+        if ( (*ptr = alloc_xenheap_page()) == NULL )
             return -ENOMEM;
 
+        addr = virt_to_maddr(*ptr);
+
         switch ( type )
         {
         case VMX_MSR_HOST:
-            __vmwrite(VM_EXIT_MSR_LOAD_ADDR, virt_to_maddr(*msr_area));
+            __vmwrite(VM_EXIT_MSR_LOAD_ADDR, addr);
             break;
 
         case VMX_MSR_GUEST:
-            __vmwrite(VM_EXIT_MSR_STORE_ADDR, virt_to_maddr(*msr_area));
-            __vmwrite(VM_ENTRY_MSR_LOAD_ADDR, virt_to_maddr(*msr_area));
+            __vmwrite(VM_EXIT_MSR_STORE_ADDR, addr);
+            __vmwrite(VM_ENTRY_MSR_LOAD_ADDR, addr);
             break;
         }
     }
 
-    for ( idx = 0; idx < *msr_count; idx++ )
-        if ( (*msr_area)[idx].index == msr )
+    start = *ptr;
+    end   = start + total;
+
+    for ( ent = start; ent < end && ent->index <= msr; ++ent )
+        if ( ent->index == msr )
             return 0;
 
-    if ( *msr_count == (PAGE_SIZE / sizeof(struct vmx_msr_entry)) )
+    if ( total == (PAGE_SIZE / sizeof(*ent)) )
         return -ENOSPC;
 
-    msr_area_elem = *msr_area + *msr_count;
-    msr_area_elem->index = msr;
-    msr_area_elem->mbz = 0;
+    memmove(ent + 1, ent, sizeof(*ent) * (end - ent));
 
-    ++*msr_count;
+    ent->index = msr;
+    ent->mbz = 0;
 
     switch ( type )
     {
     case VMX_MSR_HOST:
-        rdmsrl(msr, msr_area_elem->data);
-        __vmwrite(VM_EXIT_MSR_LOAD_COUNT, *msr_count);
+        rdmsrl(msr, ent->data);
+        __vmwrite(VM_EXIT_MSR_LOAD_COUNT, ++vmx->host_msr_count);
         break;
 
     case VMX_MSR_GUEST:
-        msr_area_elem->data = 0;
-        __vmwrite(VM_EXIT_MSR_STORE_COUNT, *msr_count);
-        __vmwrite(VM_ENTRY_MSR_LOAD_COUNT, *msr_count);
+        ent->data = 0;
+        __vmwrite(VM_EXIT_MSR_STORE_COUNT, ++vmx->msr_count);
+        __vmwrite(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_count);
         break;
     }