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[Xen-devel] [PATCH 38/60] 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@xxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
RFC V2: split off non-refactoring part
V1: constify pointers, use initializers (Jan Beulich)
---
 xen/arch/x86/domain.c | 57 +++++++++++++++++++++++++++++++--------------------
 1 file changed, 35 insertions(+), 22 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index d3ee699da6..adc06154ee 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1626,6 +1626,37 @@ static inline bool need_full_gdt(const struct domain *d)
     return is_pv_domain(d) && !is_idle_domain(d);
 }
 
+static inline 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 inline 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 inline 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();
@@ -1634,7 +1665,6 @@ 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));
@@ -1676,25 +1706,13 @@ 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);
 
@@ -1707,12 +1725,7 @@ 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);
-- 
2.16.4


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