[PATCH 1/3] x86,vdso: Change the PER_CPU segment to use struct desc_struct

Andy Lutomirski
2014-07-26T01:13:20Z

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>
---
arch/x86/kernel/vsyscall_64.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index e1e1e80..158cdff 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -289,7 +289,7 @@ sigsegv:
*/
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);
@@ -298,13 +298,17 @@ 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;
+ memset(&d, 0, sizeof(d));
+ d.limit0 = cpu | ((node & 0xf) << 12);
+ d.limit = node >> 4;
+ d.type = 4; /* RO data, expand down */
+ d.dpl = 3; /* Visible to user code */
+ d.s = 1; /* Non a system segment */
+ d.p = 1; /* Present */

write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
}
--
1.9.3