x86/fpu: Don't abuse FPU in kernel threads if use_eager_fpu() (110d7f75) · Commits · 戴 / test

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>

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);
		}

		/*

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