Commit 060aa16f authored by Thomas Gleixner's avatar Thomas Gleixner
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x86/ioperm: Add bitmap sequence number 



Add a globally unique sequence number which is incremented when ioperm() is
changing the I/O bitmap of a task. Store the new sequence number in the
io_bitmap structure and compare it with the sequence number of the I/O
bitmap which was last loaded on a CPU. Only update the bitmap if the
sequence is different.

That should further reduce the overhead of I/O bitmap scheduling when there
are only a few I/O bitmap users on the system.

The 64bit sequence counter is sufficient. A wraparound of the sequence
counter assuming an ioperm() call every nanosecond would require about 584
years of uptime.

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 577d5cd7

arch/x86/include/asm/io_bitmap.h

+1 −0
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
#include <asm/processor.h>



struct io_bitmap {

	u64		sequence;

	/* The maximum number of bytes to copy so all zero bits are covered */

	unsigned int	max;

	unsigned long	bitmap[IO_BITMAP_LONGS];

arch/x86/include/asm/processor.h

+3 −0
Original line number Diff line number Diff line
@@ -361,6 +361,9 @@ struct entry_stack_page { 
 * All IO bitmap related data stored in the TSS:

 */

struct x86_io_bitmap {

	/* The sequence number of the last active bitmap. */

	u64			prev_sequence;



	/*

	 * Store the dirty size of the last io bitmap offender. The next

	 * one will have to do the cleanup as the switch out to a non io

arch/x86/kernel/cpu/common.c

+1 −0
Original line number Diff line number Diff line
@@ -1862,6 +1862,7 @@ void cpu_init(void) 
	tss_setup_ist(tss);

	tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;

	tss->io_bitmap.prev_max = 0;

	tss->io_bitmap.prev_sequence = 0;

	memset(tss->io_bitmap.bitmap, 0xff, sizeof(tss->io_bitmap.bitmap));

	set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);

arch/x86/kernel/ioport.c

+5 −0
Original line number Diff line number Diff line
@@ -14,6 +14,8 @@ 
#include <asm/io_bitmap.h>

#include <asm/desc.h>



static atomic64_t io_bitmap_sequence;



/*

 * this changes the io permissions bitmap in the current task.

 */
@@ -72,6 +74,9 @@ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on) 


	/* Update the thread data */

	iobm->max = bytes;

	/* Update the sequence number to force an update in switch_to() */

	iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);



	/*

	 * Store the bitmap pointer (might be the same if the task already

	 * head one). Set the TIF flag, just in case this is the first

arch/x86/kernel/process.c

+28 −10
Original line number Diff line number Diff line
@@ -360,6 +360,28 @@ void arch_setup_new_exec(void) 
	}

}



static void switch_to_update_io_bitmap(struct tss_struct *tss,

				       struct io_bitmap *iobm)

{

	/*

	 * Copy at least the byte range of the incoming tasks bitmap which

	 * covers the permitted I/O ports.

	 *

	 * If the previous task which used an I/O bitmap had more bits

	 * permitted, then the copy needs to cover those as well so they

	 * get turned off.

	 */

	memcpy(tss->io_bitmap.bitmap, iobm->bitmap,

	       max(tss->io_bitmap.prev_max, iobm->max));



	/*

	 * Store the new max and the sequence number of this bitmap

	 * and a pointer to the bitmap itself.

	 */

	tss->io_bitmap.prev_max = iobm->max;

	tss->io_bitmap.prev_sequence = iobm->sequence;

}



static inline void switch_to_bitmap(struct thread_struct *next,

				    unsigned long tifp, unsigned long tifn)

{
@@ -369,18 +391,14 @@ static inline void switch_to_bitmap(struct thread_struct *next, 
		struct io_bitmap *iobm = next->io_bitmap;



		/*

		 * Copy at least the size of the incoming tasks bitmap

		 * which covers the last permitted I/O port.

		 *

		 * If the previous task which used an io bitmap had more

		 * bits permitted, then the copy needs to cover those as

		 * well so they get turned off.

		 * Only copy bitmap data when the sequence number

		 * differs. The update time is accounted to the incoming

		 * task.

		 */

		memcpy(tss->io_bitmap.bitmap, next->io_bitmap->bitmap,

		       max(tss->io_bitmap.prev_max, next->io_bitmap->max));

		if (tss->io_bitmap.prev_sequence != iobm->sequence)

			switch_to_update_io_bitmap(tss, iobm);



		/* Store the new max and set io_bitmap_base valid */

		tss->io_bitmap.prev_max = next->io_bitmap->max;

		/* Enable the bitmap */

		tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;



		/*

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