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>

1 files changed, 12 insertions, 7 deletions

diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index a155dca5edb5..261b1349acc9 100644
--- 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);
 }