From: Kyle Huey me@kylehuey.com

commit af8b3cd3934ec60f4c2a420d19a9d416554f140b upstream

Help the compiler to avoid reevaluating the thread flags for each checked bit by reordering the bit checks and providing an explicit xor for evaluation.

With default defconfigs for each arch,

x86_64: arch/x86/kernel/process.o text data bss dec hex 3056 8577 16 11649 2d81 Before 3024 8577 16 11617 2d61 After

i386: arch/x86/kernel/process.o text data bss dec hex 2957 8673 8 11638 2d76 Before 2925 8673 8 11606 2d56 After

Originally-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Kyle Huey khuey@kylehuey.com Cc: Peter Zijlstra peterz@infradead.org Cc: Andy Lutomirski luto@kernel.org Link: http://lkml.kernel.org/r/20170214081104.9244-2-khuey@kylehuey.com Signed-off-by: Thomas Gleixner tglx@linutronix.de

[dwmw2: backported to make TIF_RDS handling simpler. No deferred TR reload.] Signed-off-by: David Woodhouse dwmw@amazon.co.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Srivatsa S. Bhat srivatsa@csail.mit.edu Reviewed-by: Matt Helsley (VMware) matt.helsley@gmail.com Reviewed-by: Alexey Makhalov amakhalov@vmware.com Reviewed-by: Bo Gan ganb@vmware.com ---

arch/x86/kernel/process.c | 54 ++++++++++++++++++++++++++------------------- 1 file changed, 31 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 7c5c5dc..cc0f288 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -188,48 +188,56 @@ int set_tsc_mode(unsigned int val) return 0; }

+static inline void switch_to_bitmap(struct tss_struct *tss, + struct thread_struct *prev, + struct thread_struct *next, + unsigned long tifp, unsigned long tifn) +{ + if (tifn & _TIF_IO_BITMAP) { + /* + * Copy the relevant range of the IO bitmap. + * Normally this is 128 bytes or less: + */ + memcpy(tss->io_bitmap, next->io_bitmap_ptr, + max(prev->io_bitmap_max, next->io_bitmap_max)); + } else if (tifp & _TIF_IO_BITMAP) { + /* + * Clear any possible leftover bits: + */ + memset(tss->io_bitmap, 0xff, prev->io_bitmap_max); + } +} + void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p, struct tss_struct *tss) { struct thread_struct *prev, *next; + unsigned long tifp, tifn;

prev = &prev_p->thread; next = &next_p->thread;

- if (test_tsk_thread_flag(prev_p, TIF_BLOCKSTEP) ^ - test_tsk_thread_flag(next_p, TIF_BLOCKSTEP)) { + tifn = READ_ONCE(task_thread_info(next_p)->flags); + tifp = READ_ONCE(task_thread_info(prev_p)->flags); + switch_to_bitmap(tss, prev, next, tifp, tifn); + + propagate_user_return_notify(prev_p, next_p); + + if ((tifp ^ tifn) & _TIF_BLOCKSTEP) { unsigned long debugctl = get_debugctlmsr();

debugctl &= ~DEBUGCTLMSR_BTF; - if (test_tsk_thread_flag(next_p, TIF_BLOCKSTEP)) + if (tifn & _TIF_BLOCKSTEP) debugctl |= DEBUGCTLMSR_BTF; - update_debugctlmsr(debugctl); }

- if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^ - test_tsk_thread_flag(next_p, TIF_NOTSC)) { - /* prev and next are different */ - if (test_tsk_thread_flag(next_p, TIF_NOTSC)) + if ((tifp ^ tifn) & _TIF_NOTSC) { + if (tifn & _TIF_NOTSC) hard_disable_TSC(); else hard_enable_TSC(); } - - if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) { - /* - * Copy the relevant range of the IO bitmap. - * Normally this is 128 bytes or less: - */ - memcpy(tss->io_bitmap, next->io_bitmap_ptr, - max(prev->io_bitmap_max, next->io_bitmap_max)); - } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) { - /* - * Clear any possible leftover bits: - */ - memset(tss->io_bitmap, 0xff, prev->io_bitmap_max); - } - propagate_user_return_notify(prev_p, next_p); }

/*