[PATCH 2/2] i386 TIF flags for debug regs and io bitmap in ctxsw

[PATCH 2/2] i386 TIF flags for debug regs and io bitmap in ctxsw

[Stephane Eranian]

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 i386 modifications.

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

diff -urNp linux-2.6.17.2.orig/arch/i386/kernel/ioport.c linux-2.6.17.2-tif/arch/i386/kernel/ioport.c
--- linux-2.6.17.2.orig/arch/i386/kernel/ioport.c	2006-06-17 18:49:35.000000000 -0700
+++ linux-2.6.17.2-tif/arch/i386/kernel/ioport.c	2006-07-03 09:28:07.000000000 -0700
@@ -79,6 +79,7 @@ asmlinkage long sys_ioperm(unsigned long
 
 		memset(bitmap, 0xff, IO_BITMAP_BYTES);
 		t->io_bitmap_ptr = bitmap;
+		set_thread_flag(TIF_IO_BITMAP);
 	}
 
 	/*
diff -urNp linux-2.6.17.2.orig/arch/i386/kernel/process.c linux-2.6.17.2-tif/arch/i386/kernel/process.c
--- linux-2.6.17.2.orig/arch/i386/kernel/process.c	2006-06-17 18:49:35.000000000 -0700
+++ linux-2.6.17.2-tif/arch/i386/kernel/process.c	2006-07-04 00:06:16.000000000 -0700
@@ -370,6 +370,7 @@ 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:
 		 */
@@ -388,6 +389,7 @@ void flush_thread(void)
 
 	memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);
 	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));	
+	clear_tsk_thread_flag(tsk, TIF_DEBUG);
 	/*
 	 * Forget coprocessor state..
 	 */
@@ -432,7 +434,7 @@ int copy_thread(int nr, unsigned long cl
 	savesegment(gs,p->thread.gs);
 
 	tsk = current;
-	if (unlikely(NULL != tsk->thread.io_bitmap_ptr)) {
+	if (unlikely(test_tsk_thread_flag(tsk, 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;
@@ -440,6 +442,7 @@ int copy_thread(int nr, unsigned long cl
 		}
 		memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
 			IO_BITMAP_BYTES);
+		set_tsk_thread_flag(p, TIF_IO_BITMAP);
 	}
 
 	/*
@@ -534,10 +537,24 @@ int dump_task_regs(struct task_struct *t
 	return 1;
 }
 
-static inline void
-handle_io_bitmap(struct thread_struct *next, struct tss_struct *tss)
+static inline void __switch_to_xtra(struct task_struct *next_p,
+				    struct tss_struct *tss)
 {
-	if (!next->io_bitmap_ptr) {
+	struct thread_struct *next;
+
+	next = &next_p->thread;
+
+	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
+		set_debugreg(next->debugreg[0], 0);
+		set_debugreg(next->debugreg[1], 1);
+		set_debugreg(next->debugreg[2], 2);
+		set_debugreg(next->debugreg[3], 3);
+		/* no 4 and 5 */
+		set_debugreg(next->debugreg[6], 6);
+		set_debugreg(next->debugreg[7], 7);
+	}
+
+	if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP) == 0) {
 		/*
 		 * Disable the bitmap via an invalid offset. We still cache
 		 * the previous bitmap owner and the IO bitmap contents:
@@ -545,6 +562,7 @@ handle_io_bitmap(struct thread_struct *n
 		tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
 		return;
 	}
+
 	if (likely(next == tss->io_bitmap_owner)) {
 		/*
 		 * Previous owner of the bitmap (hence the bitmap content)
@@ -674,18 +692,9 @@ struct task_struct fastcall * __switch_t
 	/*
 	 * Now maybe reload the debug registers
 	 */
-	if (unlikely(next->debugreg[7])) {
-		set_debugreg(next->debugreg[0], 0);
-		set_debugreg(next->debugreg[1], 1);
-		set_debugreg(next->debugreg[2], 2);
-		set_debugreg(next->debugreg[3], 3);
-		/* no 4 and 5 */
-		set_debugreg(next->debugreg[6], 6);
-		set_debugreg(next->debugreg[7], 7);
-	}
-
-	if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr))
-		handle_io_bitmap(next, tss);
+	if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
+	    || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
+		__switch_to_xtra(next_p, tss);
 
 	disable_tsc(prev_p, next_p);
 
diff -urNp linux-2.6.17.2.orig/arch/i386/kernel/ptrace.c linux-2.6.17.2-tif/arch/i386/kernel/ptrace.c
--- linux-2.6.17.2.orig/arch/i386/kernel/ptrace.c	2006-06-17 18:49:35.000000000 -0700
+++ linux-2.6.17.2-tif/arch/i386/kernel/ptrace.c	2006-07-04 00:19:59.000000000 -0700
@@ -468,8 +468,11 @@ long arch_ptrace(struct task_struct *chi
 				  for(i=0; i<4; i++)
 					  if ((0x5f54 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
 						  goto out_tsk;
+				  if (data)
+					  set_tsk_thread_flag(child, TIF_DEBUG);
+				  else
+					  clear_tsk_thread_flag(child, TIF_DEBUG);
 			  }
-
 			  addr -= (long) &dummy->u_debugreg;
 			  addr = addr >> 2;
 			  child->thread.debugreg[addr] = data;
diff -urNp linux-2.6.17.2.orig/include/asm-i386/thread_info.h linux-2.6.17.2-tif/include/asm-i386/thread_info.h
--- linux-2.6.17.2.orig/include/asm-i386/thread_info.h	2006-06-17 18:49:35.000000000 -0700
+++ linux-2.6.17.2-tif/include/asm-i386/thread_info.h	2006-07-03 05:51:25.000000000 -0700
@@ -143,6 +143,8 @@ register unsigned long current_stack_poi
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal() */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17
+#define TIF_DEBUG		18	/* uses debug registers */
+#define TIF_IO_BITMAP		19	/* uses I/O bitmap */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
@@ -155,6 +157,8 @@ register unsigned long current_stack_poi
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#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 \
@@ -163,6 +167,9 @@ register unsigned long current_stack_poi
 /* work to do on any return to u-space */
 #define _TIF_ALLWORK_MASK	(0x0000FFFF & ~_TIF_SECCOMP)
 
+/* flags to check in __switch_to() */
+#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)
+
 /*
  * Thread-synchronous status.
  *

[PATCH] i386 TIF flags for debug regs and io bitmap in ctxsw (v2)

[Stephane Eranian]

Hello,

Here is the second version of my TIF flag patch for i386.
This version incoporates the changes suggested by Chuck. 

This patch is against mainline.

This patch covers the i386 modifications.
 
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

diff --git a/arch/i386/kernel/ioport.c b/arch/i386/kernel/ioport.c
--- a/arch/i386/kernel/ioport.c
+++ b/arch/i386/kernel/ioport.c
@@ -79,6 +79,7 @@ asmlinkage long sys_ioperm(unsigned long
 
 		memset(bitmap, 0xff, IO_BITMAP_BYTES);
 		t->io_bitmap_ptr = bitmap;
+		set_thread_flag(TIF_IO_BITMAP);
 	}
 
 	/*
diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -359,16 +359,16 @@ EXPORT_SYMBOL(kernel_thread);
  */
 void exit_thread(void)
 {
-	struct task_struct *tsk = current;
-	struct thread_struct *t = &tsk->thread;
-
 	/* The process may have allocated an io port bitmap... nuke it. */
-	if (unlikely(NULL != t->io_bitmap_ptr)) {
+	if (unlikely(test_thread_flag(TIF_IO_BITMAP))) {
+		struct task_struct *tsk = current;
+		struct thread_struct *t = &tsk->thread;
 		int cpu = get_cpu();
 		struct tss_struct *tss = &per_cpu(init_tss, cpu);
 
 		kfree(t->io_bitmap_ptr);
 		t->io_bitmap_ptr = NULL;
+		clear_thread_flag(TIF_IO_BITMAP);
 		/*
 		 * Careful, clear this in the TSS too:
 		 */
@@ -387,6 +387,7 @@ void flush_thread(void)
 
 	memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);
 	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));	
+	clear_tsk_thread_flag(tsk, TIF_DEBUG);
 	/*
 	 * Forget coprocessor state..
 	 */
@@ -431,7 +432,7 @@ int copy_thread(int nr, unsigned long cl
 	savesegment(gs,p->thread.gs);
 
 	tsk = current;
-	if (unlikely(NULL != tsk->thread.io_bitmap_ptr)) {
+	if (unlikely(test_tsk_thread_flag(tsk, 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;
@@ -439,6 +440,7 @@ int copy_thread(int nr, unsigned long cl
 		}
 		memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
 			IO_BITMAP_BYTES);
+		set_tsk_thread_flag(p, TIF_IO_BITMAP);
 	}
 
 	/*
@@ -533,10 +535,24 @@ int dump_task_regs(struct task_struct *t
 	return 1;
 }
 
-static inline void
-handle_io_bitmap(struct thread_struct *next, struct tss_struct *tss)
+static inline void __switch_to_xtra(struct task_struct *next_p,
+				    struct tss_struct *tss)
 {
-	if (!next->io_bitmap_ptr) {
+	struct thread_struct *next;
+
+	next = &next_p->thread;
+
+	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
+		set_debugreg(next->debugreg[0], 0);
+		set_debugreg(next->debugreg[1], 1);
+		set_debugreg(next->debugreg[2], 2);
+		set_debugreg(next->debugreg[3], 3);
+		/* no 4 and 5 */
+		set_debugreg(next->debugreg[6], 6);
+		set_debugreg(next->debugreg[7], 7);
+	}
+
+	if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
 		/*
 		 * Disable the bitmap via an invalid offset. We still cache
 		 * the previous bitmap owner and the IO bitmap contents:
@@ -544,6 +560,7 @@ handle_io_bitmap(struct thread_struct *n
 		tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
 		return;
 	}
+
 	if (likely(next == tss->io_bitmap_owner)) {
 		/*
 		 * Previous owner of the bitmap (hence the bitmap content)
@@ -673,18 +690,9 @@ struct task_struct fastcall * __switch_t
 	/*
 	 * Now maybe reload the debug registers
 	 */
-	if (unlikely(next->debugreg[7])) {
-		set_debugreg(next->debugreg[0], 0);
-		set_debugreg(next->debugreg[1], 1);
-		set_debugreg(next->debugreg[2], 2);
-		set_debugreg(next->debugreg[3], 3);
-		/* no 4 and 5 */
-		set_debugreg(next->debugreg[6], 6);
-		set_debugreg(next->debugreg[7], 7);
-	}
-
-	if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr))
-		handle_io_bitmap(next, tss);
+	if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
+	    || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
+		__switch_to_xtra(next_p, tss);
 
 	disable_tsc(prev_p, next_p);
 
diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
--- a/arch/i386/kernel/ptrace.c
+++ b/arch/i386/kernel/ptrace.c
@@ -468,8 +468,11 @@ long arch_ptrace(struct task_struct *chi
 				  for(i=0; i<4; i++)
 					  if ((0x5f54 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
 						  goto out_tsk;
+				  if (data)
+					  set_tsk_thread_flag(child, TIF_DEBUG);
+				  else
+					  clear_tsk_thread_flag(child, TIF_DEBUG);
 			  }
-
 			  addr -= (long) &dummy->u_debugreg;
 			  addr = addr >> 2;
 			  child->thread.debugreg[addr] = data;
diff --git a/include/asm-i386/thread_info.h b/include/asm-i386/thread_info.h
--- a/include/asm-i386/thread_info.h
+++ b/include/asm-i386/thread_info.h
@@ -140,6 +140,8 @@ static inline struct thread_info *curren
 #define TIF_SECCOMP		8	/* secure computing */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal() */
 #define TIF_MEMDIE		16
+#define TIF_DEBUG		17	/* uses debug registers */
+#define TIF_IO_BITMAP		18	/* uses I/O bitmap */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
@@ -151,6 +153,8 @@ static inline struct thread_info *curren
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#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 \
@@ -159,6 +163,9 @@ static inline struct thread_info *curren
 /* work to do on any return to u-space */
 #define _TIF_ALLWORK_MASK	(0x0000FFFF & ~_TIF_SECCOMP)
 
+/* flags to check in __switch_to() */
+#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)
+
 /*
  * Thread-synchronous status.
  *

Re: [PATCH] i386 TIF flags for debug regs and io bitmap in ctxsw (v2)

[Stephane Eranian]

Hello,

I would like to follow-up the TIF flags and especially on the
rules of inheritance. It appears the TIF flags are copied from
parent to child task systematically on copy_process.
Then they are adjusted in copy_threads() or sub-functions.

The TIF_IO_BITMAP is checked in copy_threads() with the following code:

int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
	unsigned long unused,
	struct task_struct * p, struct pt_regs * regs)
{
	....
	if (unlikely(test_tsk_thread_flag(tsk, 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;
			return -ENOMEM;
		}
		memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
			IO_BITMAP_BYTES);
		set_tsk_thread_flag(p, TIF_IO_BITMAP);
	}

I would think that the set_tsk_thread_flag() is extraneous.

As for TIF_DEBUG, my patch is not clearing it. I don't think you can
have HW breakpoints be inherited from one task to the other.

Any comments on this?


On Wed, Jul 05, 2006 at 04:54:06AM -0700, Stephane Eranian wrote:
> Hello,
> 
> Here is the second version of my TIF flag patch for i386.
> This version incoporates the changes suggested by Chuck. 
> 
> This patch is against mainline.
> 
> This patch covers the i386 modifications.
>  
> 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
> 
> diff --git a/arch/i386/kernel/ioport.c b/arch/i386/kernel/ioport.c
> --- a/arch/i386/kernel/ioport.c
> +++ b/arch/i386/kernel/ioport.c
> @@ -79,6 +79,7 @@ asmlinkage long sys_ioperm(unsigned long
>  
>  		memset(bitmap, 0xff, IO_BITMAP_BYTES);
>  		t->io_bitmap_ptr = bitmap;
> +		set_thread_flag(TIF_IO_BITMAP);
>  	}
>  
>  	/*
> diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
> --- a/arch/i386/kernel/process.c
> +++ b/arch/i386/kernel/process.c
> @@ -359,16 +359,16 @@ EXPORT_SYMBOL(kernel_thread);
>   */
>  void exit_thread(void)
>  {
> -	struct task_struct *tsk = current;
> -	struct thread_struct *t = &tsk->thread;
> -
>  	/* The process may have allocated an io port bitmap... nuke it. */
> -	if (unlikely(NULL != t->io_bitmap_ptr)) {
> +	if (unlikely(test_thread_flag(TIF_IO_BITMAP))) {
> +		struct task_struct *tsk = current;
> +		struct thread_struct *t = &tsk->thread;
>  		int cpu = get_cpu();
>  		struct tss_struct *tss = &per_cpu(init_tss, cpu);
>  
>  		kfree(t->io_bitmap_ptr);
>  		t->io_bitmap_ptr = NULL;
> +		clear_thread_flag(TIF_IO_BITMAP);
>  		/*
>  		 * Careful, clear this in the TSS too:
>  		 */
> @@ -387,6 +387,7 @@ void flush_thread(void)
>  
>  	memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);
>  	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));	
> +	clear_tsk_thread_flag(tsk, TIF_DEBUG);
>  	/*
>  	 * Forget coprocessor state..
>  	 */
> @@ -431,7 +432,7 @@ int copy_thread(int nr, unsigned long cl
>  	savesegment(gs,p->thread.gs);
>  
>  	tsk = current;
> -	if (unlikely(NULL != tsk->thread.io_bitmap_ptr)) {
> +	if (unlikely(test_tsk_thread_flag(tsk, 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;
> @@ -439,6 +440,7 @@ int copy_thread(int nr, unsigned long cl
>  		}
>  		memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
>  			IO_BITMAP_BYTES);
> +		set_tsk_thread_flag(p, TIF_IO_BITMAP);
>  	}
>  
>  	/*
> @@ -533,10 +535,24 @@ int dump_task_regs(struct task_struct *t
>  	return 1;
>  }
>  
> -static inline void
> -handle_io_bitmap(struct thread_struct *next, struct tss_struct *tss)
> +static inline void __switch_to_xtra(struct task_struct *next_p,
> +				    struct tss_struct *tss)
>  {
> -	if (!next->io_bitmap_ptr) {
> +	struct thread_struct *next;
> +
> +	next = &next_p->thread;
> +
> +	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
> +		set_debugreg(next->debugreg[0], 0);
> +		set_debugreg(next->debugreg[1], 1);
> +		set_debugreg(next->debugreg[2], 2);
> +		set_debugreg(next->debugreg[3], 3);
> +		/* no 4 and 5 */
> +		set_debugreg(next->debugreg[6], 6);
> +		set_debugreg(next->debugreg[7], 7);
> +	}
> +
> +	if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
>  		/*
>  		 * Disable the bitmap via an invalid offset. We still cache
>  		 * the previous bitmap owner and the IO bitmap contents:
> @@ -544,6 +560,7 @@ handle_io_bitmap(struct thread_struct *n
>  		tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
>  		return;
>  	}
> +
>  	if (likely(next == tss->io_bitmap_owner)) {
>  		/*
>  		 * Previous owner of the bitmap (hence the bitmap content)
> @@ -673,18 +690,9 @@ struct task_struct fastcall * __switch_t
>  	/*
>  	 * Now maybe reload the debug registers
>  	 */
> -	if (unlikely(next->debugreg[7])) {
> -		set_debugreg(next->debugreg[0], 0);
> -		set_debugreg(next->debugreg[1], 1);
> -		set_debugreg(next->debugreg[2], 2);
> -		set_debugreg(next->debugreg[3], 3);
> -		/* no 4 and 5 */
> -		set_debugreg(next->debugreg[6], 6);
> -		set_debugreg(next->debugreg[7], 7);
> -	}
> -
> -	if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr))
> -		handle_io_bitmap(next, tss);
> +	if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
> +	    || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
> +		__switch_to_xtra(next_p, tss);
>  
>  	disable_tsc(prev_p, next_p);
>  
> diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
> --- a/arch/i386/kernel/ptrace.c
> +++ b/arch/i386/kernel/ptrace.c
> @@ -468,8 +468,11 @@ long arch_ptrace(struct task_struct *chi
>  				  for(i=0; i<4; i++)
>  					  if ((0x5f54 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
>  						  goto out_tsk;
> +				  if (data)
> +					  set_tsk_thread_flag(child, TIF_DEBUG);
> +				  else
> +					  clear_tsk_thread_flag(child, TIF_DEBUG);
>  			  }
> -
>  			  addr -= (long) &dummy->u_debugreg;
>  			  addr = addr >> 2;
>  			  child->thread.debugreg[addr] = data;
> diff --git a/include/asm-i386/thread_info.h b/include/asm-i386/thread_info.h
> --- a/include/asm-i386/thread_info.h
> +++ b/include/asm-i386/thread_info.h
> @@ -140,6 +140,8 @@ static inline struct thread_info *curren
>  #define TIF_SECCOMP		8	/* secure computing */
>  #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal() */
>  #define TIF_MEMDIE		16
> +#define TIF_DEBUG		17	/* uses debug registers */
> +#define TIF_IO_BITMAP		18	/* uses I/O bitmap */
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
> @@ -151,6 +153,8 @@ static inline struct thread_info *curren
>  #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
>  #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
>  #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
> +#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 \
> @@ -159,6 +163,9 @@ static inline struct thread_info *curren
>  /* work to do on any return to u-space */
>  #define _TIF_ALLWORK_MASK	(0x0000FFFF & ~_TIF_SECCOMP)
>  
> +/* flags to check in __switch_to() */
> +#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)
> +
>  /*
>   * Thread-synchronous status.
>   *

-- 

-Stephane

Re: [PATCH] i386 TIF flags for debug regs and io bitmap in ctxsw (v2)

[Stephane Eranian]

Chuck,

On Tue, Jul 25, 2006 at 03:19:49PM -0400, Chuck Ebbert wrote:
> 
> > As for TIF_DEBUG, my patch is not clearing it. I don't think you can
> > have HW breakpoints be inherited from one task to the other.
> 
> Looks like the debug regs get copied on fork and only cleared on exec
> in flush_thread().  So this should be OK.  Please doublecheck.
> 
How is this supposed to work? You can set debug registers via ptrace().
So A is ptracing B and sets up breakpoints in B. Now, if B forks C,
C inherits the breakpoints of B. But what about the ptracing and re-parenting
that is associated with this? If A does not know about C, I wonder how this
could be work and be useful?

> (The new TIF_DEBUG flag went into 2.8.18-rc, in case you didn't notice.)

I did not keep track but thanks or this update. That's great!

-- 
-Stephane

Re: [PATCH] i386 TIF flags for debug regs and io bitmap in ctxsw (v2)

[Chuck Ebbert]

In-Reply-To: <20060725055439.GA18053@frankl.hpl.hp.com>

On Mon, 24 Jul 2006 22:54:39 -0700, Stephane Eranian wrote:
>
> I would like to follow-up the TIF flags and especially on the
> rules of inheritance. It appears the TIF flags are copied from
> parent to child task systematically on copy_process.
> Then they are adjusted in copy_threads() or sub-functions.
> 
> The TIF_IO_BITMAP is checked in copy_threads() with the following code:
> 
> int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
>       unsigned long unused,
>       struct task_struct * p, struct pt_regs * regs)
> {
>       ....
>       if (unlikely(test_tsk_thread_flag(tsk, 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;
>                       return -ENOMEM;
>               }
>               memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
>                       IO_BITMAP_BYTES);
>               set_tsk_thread_flag(p, TIF_IO_BITMAP);
>       }
> 
> I would think that the set_tsk_thread_flag() is extraneous.
> 

Yeah.  But harmless.

> As for TIF_DEBUG, my patch is not clearing it. I don't think you can
> have HW breakpoints be inherited from one task to the other.

Looks like the debug regs get copied on fork and only cleared on exec
in flush_thread().  So this should be OK.  Please doublecheck.

(The new TIF_DEBUG flag went into 2.8.18-rc, in case you didn't notice.)

-- 
Chuck