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x86/ioperm: Add bitmap sequence number

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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: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Thomas Gleixner 2019-11-11 23:03:22 +01:00
parent 577d5cd7e5
commit 060aa16fdb
5 changed files with 38 additions and 10 deletions
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1
arch/x86/include/asm/io_bitmap.h
View File

@ -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];

3
arch/x86/include/asm/processor.h
View File

@ -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

1
arch/x86/kernel/cpu/common.c
View File

@ -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);

5
arch/x86/kernel/ioport.c
View File

@ -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

38
arch/x86/kernel/process.c
View File

@ -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;
/*