x86/ldt: Make modify_ldt synchronous

[linux.git] / arch / x86 / kernel / cpu / perf_event.c

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 3658de47900f9a921a0f8373db962e061d42db3a..9469dfa556074db4dff41212a4873b31d5907772 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -2179,21 +2179,25 @@ static unsigned long get_segment_base(unsigned int segment)
        int idx = segment >> 3;
 
        if ((segment & SEGMENT_TI_MASK) == SEGMENT_LDT) {
+               struct ldt_struct *ldt;
+
                if (idx > LDT_ENTRIES)
                        return 0;
 
-               if (idx > current->active_mm->context.size)
+               /* IRQs are off, so this synchronizes with smp_store_release */
+               ldt = lockless_dereference(current->active_mm->context.ldt);
+               if (!ldt || idx > ldt->size)
                        return 0;
 
-               desc = current->active_mm->context.ldt;
+               desc = &ldt->entries[idx];
        } else {
                if (idx > GDT_ENTRIES)
                        return 0;
 
-               desc = raw_cpu_ptr(gdt_page.gdt);
+               desc = raw_cpu_ptr(gdt_page.gdt) + idx;
        }
 
-       return get_desc_base(desc + idx);
+       return get_desc_base(desc);
 }
 
 #ifdef CONFIG_COMPAT