x86_64: add workaround for no %gs-based percpu

As a stopgap until Mike Travis's x86-64 gs-based percpu patches are
ready, provide workaround functions for x86_read/write_percpu for
Xen's use.

Specifically, this means that we can't really make use of vcpu
placement, because we can't use a single gs-based memory access to get
to vcpu fields.  So disable all that for now.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 13 insertions, 3 deletions

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index c97819829146..1b318e903bf6 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -39,6 +39,13 @@ static struct x8664_pda *__cpu_pda[NR_CPUS] __initdata;
 static struct x8664_pda *__cpu_pda[NR_CPUS] __read_mostly;
 #endif
 
+void __init x86_64_init_pda(void)
+{
+        _cpu_pda = __cpu_pda;
+        cpu_pda(0) = &_boot_cpu_pda;
+        pda_init(0);
+}
+
 static void __init zap_identity_mappings(void)
 {
         pgd_t *pgd = pgd_offset_k(0UL);
@@ -102,9 +109,7 @@ void __init x86_64_start_kernel(char * real_mode_data)
 
         early_printk("Kernel alive\n");
 
-        _cpu_pda = __cpu_pda;
-        cpu_pda(0) = &_boot_cpu_pda;
-        pda_init(0);
+        x86_64_init_pda();
 
         early_printk("Kernel really alive\n");
 
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index a85f447b8d00..f3f11acf7856 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -971,6 +971,7 @@ void xen_setup_vcpu_info_placement(void)
 
         /* xen_vcpu_setup managed to place the vcpu_info within the
            percpu area for all cpus, so make use of it */
+#ifdef CONFIG_X86_32
         if (have_vcpu_info_placement) {
                 printk(KERN_INFO "Xen: using vcpu_info placement\n");
 
@@ -980,6 +981,7 @@ void xen_setup_vcpu_info_placement(void)
                 pv_irq_ops.irq_enable = xen_irq_enable_direct;
                 pv_mmu_ops.read_cr2 = xen_read_cr2_direct;
         }
+#endif
 }
 
 static unsigned xen_patch(u8 type, u16 clobbers, void *insnbuf,
@@ -1000,10 +1002,12 @@ static unsigned xen_patch(u8 type, u16 clobbers, void *insnbuf,
         goto patch_site
 
         switch (type) {
+#ifdef CONFIG_X86_32
                 SITE(pv_irq_ops, irq_enable);
                 SITE(pv_irq_ops, irq_disable);
                 SITE(pv_irq_ops, save_fl);
                 SITE(pv_irq_ops, restore_fl);
+#endif /* CONFIG_X86_32 */
 #undef SITE
 
         patch_site:
@@ -1323,6 +1327,7 @@ asmlinkage void __init xen_start_kernel(void)
 #ifdef CONFIG_X86_64
         /* Disable until direct per-cpu data access. */
         have_vcpu_info_placement = 0;
+        x86_64_init_pda();
 #endif
 
         xen_smp_init();