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Commit d3a4f48d authored by Stephane Eranian's avatar Stephane Eranian Committed by Andi Kleen
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[PATCH] x86-64 TIF flags for debug regs and io bitmap in ctxsw 



Hello,

Following my discussion with Andi. Here is a patch that introduces
two new TIF flags to simplify the context switch code in __switch_to().
The idea is to minimize the number of cache lines accessed in the common
case, i.e., when neither the debug registers nor the I/O bitmap are used.

This patch covers the x86-64 modifications. A patch for i386 follows.

Changelog:
	- add TIF_DEBUG to track when debug registers are active
	- add TIF_IO_BITMAP to track when I/O bitmap is used
	- modify __switch_to() to use the new TIF flags

<signed-off-by>: eranian@hpl.hp.com

Signed-off-by: default avatarAndi Kleen <ak@suse.de>
parent 2f766d16

arch/x86_64/ia32/ptrace32.c

+4 −0
Original line number Diff line number Diff line
@@ -117,6 +117,10 @@ static int putreg32(struct task_struct *child, unsigned regno, u32 val) 
			if ((0x5454 >> ((val >> (16 + 4*i)) & 0xf)) & 1)

			       return -EIO;

		child->thread.debugreg7 = val; 

		if (val)

			set_tsk_thread_flag(child, TIF_DEBUG);

		else

			clear_tsk_thread_flag(child, TIF_DEBUG);

		break; 

		    

	default:

arch/x86_64/kernel/ioport.c

+1 −0
Original line number Diff line number Diff line
@@ -56,6 +56,7 @@ asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on) 


		memset(bitmap, 0xff, IO_BITMAP_BYTES);

		t->io_bitmap_ptr = bitmap;

		set_thread_flag(TIF_IO_BITMAP);

	}



	/*

arch/x86_64/kernel/process.c

+42 −31
Original line number Diff line number Diff line
@@ -350,6 +350,7 @@ void exit_thread(void) 


		kfree(t->io_bitmap_ptr);

		t->io_bitmap_ptr = NULL;

		clear_thread_flag(TIF_IO_BITMAP);

		/*

		 * Careful, clear this in the TSS too:

		 */
@@ -369,6 +370,7 @@ void flush_thread(void) 
		if (t->flags & _TIF_IA32)

			current_thread_info()->status |= TS_COMPAT;

	}

	t->flags &= ~_TIF_DEBUG;



	tsk->thread.debugreg0 = 0;

	tsk->thread.debugreg1 = 0;
@@ -461,7 +463,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long rsp, 
	asm("mov %%es,%0" : "=m" (p->thread.es));

	asm("mov %%ds,%0" : "=m" (p->thread.ds));



	if (unlikely(me->thread.io_bitmap_ptr != NULL)) { 

	if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {

		p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);

		if (!p->thread.io_bitmap_ptr) {

			p->thread.io_bitmap_max = 0;
@@ -469,6 +471,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long rsp, 
		}

		memcpy(p->thread.io_bitmap_ptr, me->thread.io_bitmap_ptr,

				IO_BITMAP_BYTES);

		set_tsk_thread_flag(p, TIF_IO_BITMAP);

	} 



	/*
@@ -498,6 +501,40 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long rsp, 
 */

#define loaddebug(thread,r) set_debugreg(thread->debugreg ## r, r)



static inline void __switch_to_xtra(struct task_struct *prev_p,

			     	    struct task_struct *next_p,

			     	    struct tss_struct *tss)

{

	struct thread_struct *prev, *next;



	prev = &prev_p->thread,

	next = &next_p->thread;



	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {

		loaddebug(next, 0);

		loaddebug(next, 1);

		loaddebug(next, 2);

		loaddebug(next, 3);

		/* no 4 and 5 */

		loaddebug(next, 6);

		loaddebug(next, 7);

	}



	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);

	}

}



/*

 *	switch_to(x,y) should switch tasks from x to y.

 *
@@ -586,37 +623,11 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
		  task_stack_page(next_p) + THREAD_SIZE - PDA_STACKOFFSET);



	/*

	 * Now maybe reload the debug registers

	 * Now maybe reload the debug registers and handle I/O bitmaps

	 */

	if (unlikely(next->debugreg7)) {

		loaddebug(next, 0);

		loaddebug(next, 1);

		loaddebug(next, 2);

		loaddebug(next, 3);

		/* no 4 and 5 */

		loaddebug(next, 6);

		loaddebug(next, 7);

	}





	/* 

	 * Handle the IO bitmap 

	 */ 

	if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr)) {

		if (next->io_bitmap_ptr)

			/*

			 * 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 {

			/*

			 * Clear any possible leftover bits:

			 */

			memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);

		}

	}

	if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))

	    || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))

		__switch_to_xtra(prev_p, next_p, tss);



	return prev_p;

}

arch/x86_64/kernel/ptrace.c

+6 −2
Original line number Diff line number Diff line
@@ -421,6 +421,10 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data) 
					break;

			if (i == 4) {

			  child->thread.debugreg7 = data;

			  if (data)

			  	set_tsk_thread_flag(child, TIF_DEBUG);

			  else

			  	clear_tsk_thread_flag(child, TIF_DEBUG);

			  ret = 0;

		  	}

		  break;

include/asm-x86_64/thread_info.h

+7 −0
Original line number Diff line number Diff line
@@ -120,6 +120,8 @@ static inline struct thread_info *stack_thread_info(void) 
#define TIF_FORK		18	/* ret_from_fork */

#define TIF_ABI_PENDING		19

#define TIF_MEMDIE		20

#define TIF_DEBUG		21	/* uses debug registers */

#define TIF_IO_BITMAP		22	/* uses I/O bitmap */



#define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

#define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
@@ -133,6 +135,8 @@ static inline struct thread_info *stack_thread_info(void) 
#define _TIF_IA32		(1<<TIF_IA32)

#define _TIF_FORK		(1<<TIF_FORK)

#define _TIF_ABI_PENDING	(1<<TIF_ABI_PENDING)

#define _TIF_DEBUG		(1<<TIF_DEBUG)

#define _TIF_IO_BITMAP		(1<<TIF_IO_BITMAP)



/* work to do on interrupt/exception return */

#define _TIF_WORK_MASK \
@@ -140,6 +144,9 @@ static inline struct thread_info *stack_thread_info(void) 
/* work to do on any return to user space */

#define _TIF_ALLWORK_MASK (0x0000FFFF & ~_TIF_SECCOMP)



/* flags to check in __switch_to() */

#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)



#define PREEMPT_ACTIVE     0x10000000



/*