x86/fpu: Don't abuse FPU in kernel threads if use_eager_fpu()
AFAICS, there is no reason why kernel threads should have FPU context
even if use_eager_fpu() == T. Now that interrupted_kernel_fpu_idle()
does not check __thread_has_fpu() in the use_eager_fpu() case, we
can remove the init_fpu() code from eager_fpu_init() and change
flush_thread() called by do_execve() to initialize FPU.
Note: of course, the change in flush_thread() is horrible and must be
cleanuped. We need the new helper, and flush_thread() should return the
error if init_fpu() fails.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Suresh Siddha <sbsiddha@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/20150119185212.GD16427@redhat.com
Signed-off-by: Borislav Petkov <bp@suse.de>
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ce8b103..8348037 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -130,6 +130,7 @@
flush_ptrace_hw_breakpoint(tsk);
memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
+
drop_init_fpu(tsk);
/*
* Free the FPU state for non xsave platforms. They get reallocated
@@ -137,6 +138,12 @@
*/
if (!use_eager_fpu())
free_thread_xstate(tsk);
+ else if (!used_math()) {
+ /* kthread execs. TODO: cleanup this horror. */
+ if (WARN_ON(init_fpu(current)))
+ force_sig(SIGKILL, current);
+ math_state_restore();
+ }
}
static void hard_disable_TSC(void)