1 files changed, 40 insertions, 0 deletions

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 32826791e675..0b39173dd971 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -4,6 +4,8 @@
 #include <asm/fpu/internal.h>
 #include <asm/tlbflush.h>
 
+#include <linux/sched.h>
+
 /*
  * Initialize the TS bit in CR0 according to the style of context-switches
  * we are using:
@@ -136,6 +138,43 @@ static void __init fpu__init_system_generic(void)
 unsigned int xstate_size;
 EXPORT_SYMBOL_GPL(xstate_size);
 
+/* Enforce that 'MEMBER' is the last field of 'TYPE': */
+#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
+        BUILD_BUG_ON(sizeof(TYPE) != offsetofend(TYPE, MEMBER))
+
+/*
+ * We append the 'struct fpu' to the task_struct:
+ */
+static void __init fpu__init_task_struct_size(void)
+{
+        int task_size = sizeof(struct task_struct);
+
+        /*
+         * Subtract off the static size of the register state.
+         * It potentially has a bunch of padding.
+         */
+        task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);
+
+        /*
+         * Add back the dynamically-calculated register state
+         * size.
+         */
+        task_size += xstate_size;
+
+        /*
+         * We dynamically size 'struct fpu', so we require that
+         * it be at the end of 'thread_struct' and that
+         * 'thread_struct' be at the end of 'task_struct'.  If
+         * you hit a compile error here, check the structure to
+         * see if something got added to the end.
+         */
+        CHECK_MEMBER_AT_END_OF(struct fpu, state);
+        CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
+        CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
+
+        arch_task_struct_size = task_size;
+}
+
 /*
  * Set up the xstate_size based on the legacy FPU context size.
  *
@@ -287,6 +326,7 @@ void __init fpu__init_system(struct cpuinfo_x86 *c)
         fpu__init_system_generic();
         fpu__init_system_xstate_size_legacy();
         fpu__init_system_xstate();
+        fpu__init_task_struct_size();
 
         fpu__init_system_ctx_switch();
 }