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Commit 110d7f75 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Borislav Petkov
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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: default avatarOleg Nesterov <oleg@redhat.com>
Reviewed-by: default avatarRik 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: default avatarBorislav Petkov <bp@suse.de>
parent 4b2e762e

arch/x86/kernel/process.c

+7 −0
Original line number Diff line number Diff line
@@ -130,6 +130,7 @@ void flush_thread(void) 


	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 @@ void flush_thread(void) 
	 */

	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)

arch/x86/kernel/xsave.c

+1 −12
Original line number Diff line number Diff line
@@ -688,7 +688,7 @@ void eager_fpu_init(void) 
{

	static __refdata void (*boot_func)(void) = eager_fpu_init_bp;



	clear_used_math();

	WARN_ON(used_math());

	current_thread_info()->status = 0;



	if (eagerfpu == ENABLE)
@@ -703,17 +703,6 @@ void eager_fpu_init(void) 
		boot_func();

		boot_func = NULL;

	}



	/*

	 * This is same as math_state_restore(). But use_xsave() is

	 * not yet patched to use math_state_restore().

	 */

	init_fpu(current);

	__thread_fpu_begin(current);

	if (cpu_has_xsave)

		xrstor_state(init_xstate_buf, -1);

	else

		fxrstor_checking(&init_xstate_buf->i387);

}



/*