x86/vdso: Change the PER_CPU segment to use struct desc_struct

This makes it easier to see what's going on.  It produces
exactly the same segment descriptor as the old code.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/d492f7b55136cbc60f016adae79160707b2e03b7.1411494540.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index a155dca..261b134 100644 (file)
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -248,7 +248,7 @@ __setup("vdso=", vdso_setup);
  */
 static void vsyscall_set_cpu(int cpu)
 {
-       unsigned long d;
+       struct desc_struct d;
        unsigned long node = 0;
 #ifdef CONFIG_NUMA
        node = cpu_to_node(cpu);
@@ -257,13 +257,18 @@ static void vsyscall_set_cpu(int cpu)
                write_rdtscp_aux((node << 12) | cpu);
 
        /*
-        * Store cpu number in limit so that it can be loaded quickly
-        * in user space in vgetcpu. (12 bits for the CPU and 8 bits for the node)
+        * Store cpu number in limit so that it can be loaded
+        * quickly in user space in vgetcpu. (12 bits for the CPU
+        * and 8 bits for the node)
         */
-       d = 0x0f40000000000ULL;
-       d |= cpu;
-       d |= (node & 0xf) << 12;
-       d |= (node >> 4) << 48;
+       d = (struct desc_struct) {
+               .limit0 = cpu | ((node & 0xf) << 12),
+               .limit = node >> 4,
+               .type = 4,              /* RO data, expand down */
+               .dpl = 3,               /* Visible to user code */
+               .s = 1,                 /* Not a system segment */
+               .p = 1,                 /* Present */
+       };
 
        write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
 }