x86: reduce GDT switching

Index: 2008-10-27/xen/arch/x86/cpu/common.c
===================================================================
@@ -564,7 +564,10 @@ void __cpuinit cpu_init(void)
 {
 	int cpu = smp_processor_id();
 	struct tss_struct *t = &init_tss[cpu];
-	char gdt_load[10];
+	struct desc_ptr gdt_desc = {
+		.base = (unsigned long)(this_cpu(gdt_table) - FIRST_RESERVED_GDT_ENTRY),
+		.limit = LAST_RESERVED_GDT_BYTE
+	};
 
 	if (cpu_test_and_set(cpu, cpu_initialized)) {
 		printk(KERN_WARNING "CPU#%d already initialized!\n", cpu);

@@ -578,9 +581,7 @@ void __cpuinit cpu_init(void)
 	/* Install correct page table. */
 	write_ptbase(current);
 
-	*(unsigned short *)(&gdt_load[0]) = LAST_RESERVED_GDT_BYTE;
-	*(unsigned long  *)(&gdt_load[2]) = GDT_VIRT_START(current);
-	asm volatile ( "lgdt %0" : "=m" (gdt_load) );
+	asm volatile ( "lgdt %0" : : "m" (gdt_desc) );
 
 	/* No nested task. */
 	asm volatile ("pushf ; andw $0xbfff,(%"__OP"sp) ; popf" );

Index: 2008-10-27/xen/arch/x86/domain.c
===================================================================
@@ -309,12 +309,7 @@ int vcpu_initialise(struct vcpu *v)
         if ( is_idle_domain(d) )
         {
             v->arch.schedule_tail = continue_idle_domain;
-            if ( v->vcpu_id )
-                v->arch.cr3 = d->vcpu[0]->arch.cr3;
-            else if ( !*idle_vcpu )
-                v->arch.cr3 = __pa(idle_pg_table);
-            else if ( !(v->arch.cr3 = clone_idle_pagetable(v)) )
-                return -ENOMEM;
+            v->arch.cr3           = __pa(idle_pg_table);
         }
 
         v->arch.guest_context.ctrlreg[4] =

@@ -1171,14 +1166,18 @@ static void paravirt_ctxt_switch_to(stru
     }
 }
 
+static inline int need_full_gdt(struct vcpu *v)
+{
+    return !is_hvm_vcpu(v) && !is_idle_vcpu(v);
+}
+
 static void __context_switch(void)
 {
     struct cpu_user_regs *stack_regs = guest_cpu_user_regs();
-    unsigned int          i, cpu = smp_processor_id();
+    unsigned int          cpu = smp_processor_id();
     struct vcpu          *p = per_cpu(curr_vcpu, cpu);
     struct vcpu          *n = current;
     struct desc_struct   *gdt;
-    struct page_info     *page;
     struct desc_ptr       gdt_desc;
 
     ASSERT(p != n);

@@ -1207,16 +1206,21 @@ static void __context_switch(void)
 
     gdt = !is_pv_32on64_vcpu(n) ? per_cpu(gdt_table, cpu) :
                                   per_cpu(compat_gdt_table, cpu);
-    page = virt_to_page(gdt);
-    for (i = 0; i < NR_RESERVED_GDT_PAGES; ++i)
+    if ( need_full_gdt(n) )
     {
-        l1e_write(n->domain->arch.mm_perdomain_pt +
-                  (n->vcpu_id << GDT_LDT_VCPU_SHIFT) +
-                  FIRST_RESERVED_GDT_PAGE + i,
-                  l1e_from_page(page + i, __PAGE_HYPERVISOR));
+        struct page_info *page = virt_to_page(gdt);
+        unsigned int i;
+
+        for (i = 0; i < NR_RESERVED_GDT_PAGES; ++i)
+        {
+            l1e_write(n->domain->arch.mm_perdomain_pt +
+                      (n->vcpu_id << GDT_LDT_VCPU_SHIFT) +
+                      FIRST_RESERVED_GDT_PAGE + i,
+                      l1e_from_page(page + i, __PAGE_HYPERVISOR));
+        }
     }
 
-    if ( p->vcpu_id != n->vcpu_id )
+    if ( need_full_gdt(p) && (p->vcpu_id != n->vcpu_id || !need_full_gdt(n)) )
     {
         gdt_desc.limit = LAST_RESERVED_GDT_BYTE;
         gdt_desc.base  = (unsigned long)(gdt - FIRST_RESERVED_GDT_ENTRY);

@@ -1225,8 +1229,9 @@ static void __context_switch(void)
 
     write_ptbase(n);
 
-    if ( p->vcpu_id != n->vcpu_id )
+    if ( need_full_gdt(n) && (p->vcpu_id != n->vcpu_id || !need_full_gdt(p)) )
     {
+        gdt_desc.limit = LAST_RESERVED_GDT_BYTE;
         gdt_desc.base = GDT_VIRT_START(n);
         asm volatile ( "lgdt %0" : : "m" (gdt_desc) );
     }

Index: 2008-10-27/xen/arch/x86/domain_build.c
===================================================================
@@ -197,25 +197,13 @@ static void __init process_dom0_ioports_
 /* We run on dom0's page tables for the final part of the build process. */
 static void dom0_pt_enter(struct vcpu *v)
 {
-    struct desc_ptr gdt_desc = {
-        .limit = LAST_RESERVED_GDT_BYTE,
-        .base = (unsigned long)(this_cpu(gdt_table) - FIRST_RESERVED_GDT_ENTRY)
-    };
-
-    asm volatile ( "lgdt %0" : : "m" (gdt_desc) );
     write_ptbase(v);
 }
 
 /* Return to idle domain's page tables. */
 static void dom0_pt_exit(void)
 {
-    struct desc_ptr gdt_desc = {
-        .limit = LAST_RESERVED_GDT_BYTE,
-        .base = GDT_VIRT_START(current)
-    };
-
     write_ptbase(current);
-    asm volatile ( "lgdt %0" : : "m" (gdt_desc) );
 }
 
 int __init construct_dom0(

Index: 2008-10-27/xen/arch/x86/hvm/vmx/vmcs.c
===================================================================
@@ -444,6 +444,8 @@ static void vmx_set_host_env(struct vcpu
 {
     unsigned int cpu = smp_processor_id();
 
+    __vmwrite(HOST_GDTR_BASE,
+              (unsigned long)(this_cpu(gdt_table) - FIRST_RESERVED_GDT_ENTRY));
     __vmwrite(HOST_IDTR_BASE, (unsigned long)idt_tables[cpu]);
 
     __vmwrite(HOST_TR_SELECTOR, TSS_ENTRY << 3);

@@ -541,9 +543,6 @@ static int construct_vmcs(struct vcpu *v
     __vmwrite(IO_BITMAP_A, virt_to_maddr((char *)hvm_io_bitmap + 0));
     __vmwrite(IO_BITMAP_B, virt_to_maddr((char *)hvm_io_bitmap + PAGE_SIZE));
 
-    /* Host GDTR base. */
-    __vmwrite(HOST_GDTR_BASE, GDT_VIRT_START(v));
-
     /* Host data selectors. */
     __vmwrite(HOST_SS_SELECTOR, __HYPERVISOR_DS);
     __vmwrite(HOST_DS_SELECTOR, __HYPERVISOR_DS);

Index: 2008-10-27/xen/arch/x86/setup.c
===================================================================
@@ -230,7 +230,6 @@ static void __init percpu_init_areas(voi
 static void __init init_idle_domain(void)
 {
     struct domain *idle_domain;
-    unsigned int i;
 
     /* Domain creation requires that scheduler structures are initialised. */
     scheduler_init();

@@ -243,12 +242,6 @@ static void __init init_idle_domain(void
     idle_vcpu[0] = this_cpu(curr_vcpu) = current;
 
     setup_idle_pagetable();
-
-    for (i = 0; i < NR_RESERVED_GDT_PAGES; ++i)
-        idle_domain->arch.mm_perdomain_pt[FIRST_RESERVED_GDT_PAGE + i] =
-            l1e_from_page(virt_to_page(boot_cpu_gdt_table) + i,
-                          __PAGE_HYPERVISOR);
-
 }
 
 static void __init srat_detect_node(int cpu)

@@ -456,6 +449,7 @@ void __init __start_xen(unsigned long mb
     parse_video_info();
 
     set_current((struct vcpu *)0xfffff000); /* debug sanity */
+    idle_vcpu[0] = current;
     set_processor_id(0); /* needed early, for smp_processor_id() */
     if ( cpu_has_efer )
         rdmsrl(MSR_EFER, this_cpu(efer));

Index: 2008-10-27/xen/arch/x86/smpboot.c
===================================================================
@@ -821,7 +821,7 @@ static int __devinit do_boot_cpu(int api
  */
 {
 	unsigned long boot_error;
-	unsigned int i;
+	unsigned int order;
 	int timeout;
 	unsigned long start_eip;
 	unsigned short nmi_high = 0, nmi_low = 0;

@@ -857,21 +857,21 @@ static int __devinit do_boot_cpu(int api
 
 	gdt = per_cpu(gdt_table, cpu);
 	if (gdt == boot_cpu_gdt_table) {
-		i = get_order_from_pages(NR_RESERVED_GDT_PAGES);
+		order = get_order_from_pages(NR_RESERVED_GDT_PAGES);
 #ifdef __x86_64__
 #ifdef CONFIG_COMPAT
-		page = alloc_domheap_pages(NULL, i,
+		page = alloc_domheap_pages(NULL, order,
 					   MEMF_node(cpu_to_node(cpu)));
 		per_cpu(compat_gdt_table, cpu) = gdt = page_to_virt(page);
 		memcpy(gdt, boot_cpu_compat_gdt_table,
 		       NR_RESERVED_GDT_PAGES * PAGE_SIZE);
 		gdt[PER_CPU_GDT_ENTRY - FIRST_RESERVED_GDT_ENTRY].a = cpu;
 #endif
-		page = alloc_domheap_pages(NULL, i,
+		page = alloc_domheap_pages(NULL, order,
 					   MEMF_node(cpu_to_node(cpu)));
 		per_cpu(gdt_table, cpu) = gdt = page_to_virt(page);
 #else
-		per_cpu(gdt_table, cpu) = gdt = alloc_xenheap_pages(i);
+		per_cpu(gdt_table, cpu) = gdt = alloc_xenheap_pages(order);
 #endif
 		memcpy(gdt, boot_cpu_gdt_table,
 		       NR_RESERVED_GDT_PAGES * PAGE_SIZE);

@@ -879,13 +879,6 @@ static int __devinit do_boot_cpu(int api
 		gdt[PER_CPU_GDT_ENTRY - FIRST_RESERVED_GDT_ENTRY].a = cpu;
 	}
 
-	for (i = 0; i < NR_RESERVED_GDT_PAGES; ++i)
-		v->domain->arch.mm_perdomain_pt
-			[(v->vcpu_id << GDT_LDT_VCPU_SHIFT) +
-			 FIRST_RESERVED_GDT_PAGE + i]
-			= l1e_from_page(virt_to_page(gdt) + i,
-					__PAGE_HYPERVISOR);
-
 #ifdef __i386__
 	if (!per_cpu(doublefault_tss, cpu)) {
 		per_cpu(doublefault_tss, cpu) = alloc_xenheap_page();

Index: 2008-10-27/xen/arch/x86/x86_32/mm.c
===================================================================
@@ -135,30 +135,6 @@ void __init setup_idle_pagetable(void)
                                 __PAGE_HYPERVISOR));
 }
 
-unsigned long clone_idle_pagetable(struct vcpu *v)
-{
-    unsigned int i;
-    struct domain *d = v->domain;
-    l3_pgentry_t *l3_table = v->arch.pae_l3_cache.table[0];
-    l2_pgentry_t *l2_table = alloc_xenheap_page();
-
-    if ( !l2_table )
-        return 0;
-
-    memcpy(l3_table, idle_pg_table, L3_PAGETABLE_ENTRIES * sizeof(*l3_table));
-    l3_table[l3_table_offset(PERDOMAIN_VIRT_START)] =
-        l3e_from_page(virt_to_page(l2_table), _PAGE_PRESENT);
-
-    copy_page(l2_table, idle_pg_table_l2 +
-              l3_table_offset(PERDOMAIN_VIRT_START) * L2_PAGETABLE_ENTRIES);
-    for ( i = 0; i < PDPT_L2_ENTRIES; ++i )
-        l2_table[l2_table_offset(PERDOMAIN_VIRT_START) + i] =
-            l2e_from_page(virt_to_page(d->arch.mm_perdomain_pt) + i,
-                          __PAGE_HYPERVISOR);
-
-    return __pa(l3_table);
-}
-
 void __init zap_low_mappings(l2_pgentry_t *dom0_l2)
 {
     int i;

Index: 2008-10-27/xen/arch/x86/x86_64/mm.c
===================================================================
@@ -21,7 +21,6 @@
 #include <xen/lib.h>
 #include <xen/init.h>
 #include <xen/mm.h>
-#include <xen/numa.h>
 #include <xen/sched.h>
 #include <xen/guest_access.h>
 #include <asm/current.h>

@@ -210,24 +209,6 @@ void __init setup_idle_pagetable(void)
                   __PAGE_HYPERVISOR));
 }
 
-unsigned long clone_idle_pagetable(struct vcpu *v)
-{
-    struct domain *d = v->domain;
-    struct page_info *page = alloc_domheap_page(NULL,
-                                                MEMF_node(vcpu_to_node(v)));
-    l4_pgentry_t *l4_table = page_to_virt(page);
-
-    if ( !page )
-        return 0;
-
-    copy_page(l4_table, idle_pg_table);
-    l4_table[l4_table_offset(PERDOMAIN_VIRT_START)] =
-        l4e_from_page(virt_to_page(d->arch.mm_perdomain_l3),
-                      __PAGE_HYPERVISOR);
-
-    return __pa(l4_table);
-}
-
 void __init zap_low_mappings(void)
 {
     BUG_ON(num_online_cpus() != 1);

Index: 2008-10-27/xen/include/asm-x86/page.h
===================================================================
@@ -278,7 +278,6 @@ extern unsigned int   m2p_compat_vstart;
 #endif
 void paging_init(void);
 void setup_idle_pagetable(void);
-unsigned long clone_idle_pagetable(struct vcpu *);
 #endif /* !defined(__ASSEMBLY__) */
 
 #define _PAGE_PRESENT  0x001U