x86/entry/64: Make cpu_entry_area.tss read-only

[mirror_ubuntu-artful-kernel.git] / arch / x86 / include / asm / fixmap.h

diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index 953aed54cb5e3110a77f7c48dd0dd72cec5ba1b4..5dc269ff408556a45ed313d202d064544f8fa188 100644 (file)
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -56,9 +56,14 @@ struct cpu_entry_area {
        char gdt[PAGE_SIZE];
 
        /*
-        * The GDT is just below cpu_tss and thus serves (on x86_64) as a
-        * a read-only guard page for the SYSENTER stack at the bottom
-        * of the TSS region.
+        * The GDT is just below SYSENTER_stack and thus serves (on x86_64) as
+        * a a read-only guard page.
+        */
+       struct SYSENTER_stack_page SYSENTER_stack_page;
+
+       /*
+        * On x86_64, the TSS is mapped RO.  On x86_32, it's mapped RW because
+        * we need task switches to work, and task switches write to the TSS.
         */
        struct tss_struct tss;
 
@@ -225,5 +230,10 @@ static inline struct cpu_entry_area *get_cpu_entry_area(int cpu)
        return (struct cpu_entry_area *)__fix_to_virt(__get_cpu_entry_area_page_index(cpu, 0));
 }
 
+static inline struct SYSENTER_stack *cpu_SYSENTER_stack(int cpu)
+{
+       return &get_cpu_entry_area(cpu)->SYSENTER_stack_page.stack;
+}
+
 #endif /* !__ASSEMBLY__ */
 #endif /* _ASM_X86_FIXMAP_H */