x86: make loading of GDT at context switch more modular

In preparation for core scheduling, carve out the GDT related
functionality (writing GDT related PTEs, loading default of full GDT)
into sub-functions.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 894d8673e2c0f564155540c4ac5ac11755e137d9..84cafbe5584f7c74ddf9ed543240e7c34465d6a7 100644 (file)
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1640,6 +1640,37 @@ static inline bool need_full_gdt(const struct domain *d)
     return is_pv_domain(d) && !is_idle_domain(d);
 }
 
+static void write_full_gdt_ptes(seg_desc_t *gdt, const struct vcpu *v)
+{
+    unsigned long mfn = virt_to_mfn(gdt);
+    l1_pgentry_t *pl1e = pv_gdt_ptes(v);
+    unsigned int i;
+
+    for ( i = 0; i < NR_RESERVED_GDT_PAGES; i++ )
+        l1e_write(pl1e + FIRST_RESERVED_GDT_PAGE + i,
+                  l1e_from_pfn(mfn + i, __PAGE_HYPERVISOR_RW));
+}
+
+static void load_full_gdt(const struct vcpu *v, unsigned int cpu)
+{
+    struct desc_ptr gdt_desc = {
+        .limit = LAST_RESERVED_GDT_BYTE,
+        .base = GDT_VIRT_START(v),
+    };
+
+    lgdt(&gdt_desc);
+}
+
+static void load_default_gdt(const seg_desc_t *gdt, unsigned int cpu)
+{
+    struct desc_ptr gdt_desc = {
+        .limit = LAST_RESERVED_GDT_BYTE,
+        .base  = (unsigned long)(gdt - FIRST_RESERVED_GDT_ENTRY),
+    };
+
+    lgdt(&gdt_desc);
+}
+
 static void __context_switch(void)
 {
     struct cpu_user_regs *stack_regs = guest_cpu_user_regs();
@@ -1648,7 +1679,6 @@ static void __context_switch(void)
     struct vcpu          *n = current;
     struct domain        *pd = p->domain, *nd = n->domain;
     seg_desc_t           *gdt;
-    struct desc_ptr       gdt_desc;
 
     ASSERT(p != n);
     ASSERT(!vcpu_cpu_dirty(n));
@@ -1690,25 +1720,13 @@ static void __context_switch(void)
 
     gdt = !is_pv_32bit_domain(nd) ? per_cpu(gdt_table, cpu) :
                                     per_cpu(compat_gdt_table, cpu);
-    if ( need_full_gdt(nd) )
-    {
-        unsigned long mfn = virt_to_mfn(gdt);
-        l1_pgentry_t *pl1e = pv_gdt_ptes(n);
-        unsigned int i;
 
-        for ( i = 0; i < NR_RESERVED_GDT_PAGES; i++ )
-            l1e_write(pl1e + FIRST_RESERVED_GDT_PAGE + i,
-                      l1e_from_pfn(mfn + i, __PAGE_HYPERVISOR_RW));
-    }
+    if ( need_full_gdt(nd) )
+        write_full_gdt_ptes(gdt, n);
 
     if ( need_full_gdt(pd) &&
          ((p->vcpu_id != n->vcpu_id) || !need_full_gdt(nd)) )
-    {
-        gdt_desc.limit = LAST_RESERVED_GDT_BYTE;
-        gdt_desc.base  = (unsigned long)(gdt - FIRST_RESERVED_GDT_ENTRY);
-
-        lgdt(&gdt_desc);
-    }
+        load_default_gdt(gdt, cpu);
 
     write_ptbase(n);
 
@@ -1721,12 +1739,7 @@ static void __context_switch(void)
 
     if ( need_full_gdt(nd) &&
          ((p->vcpu_id != n->vcpu_id) || !need_full_gdt(pd)) )
-    {
-        gdt_desc.limit = LAST_RESERVED_GDT_BYTE;
-        gdt_desc.base = GDT_VIRT_START(n);
-
-        lgdt(&gdt_desc);
-    }
+        load_full_gdt(n, cpu);
 
     if ( pd != nd )
         cpumask_clear_cpu(cpu, pd->dirty_cpumask);