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Subject[patch V3 11/20] x86/ioperm: Add bitmap sequence number
From: Thomas Gleixner <tglx@linutronix.de>

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>

---
V3: Remove the pointer comparison (Peter, Andy)

V2: New patch
---
arch/x86/include/asm/io_bitmap.h | 1 +
arch/x86/include/asm/processor.h | 3 +++
arch/x86/kernel/cpu/common.c | 1 +
arch/x86/kernel/ioport.c | 5 +++++
arch/x86/kernel/process.c | 38 ++++++++++++++++++++++++++++----------
5 files changed, 38 insertions(+), 10 deletions(-)

--- a/arch/x86/include/asm/io_bitmap.h
+++ b/arch/x86/include/asm/io_bitmap.h
@@ -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];
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -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
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -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);

--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -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, uns

/* 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
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -354,6 +354,28 @@ 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)
{
@@ -363,18 +385,14 @@ static inline void switch_to_bitmap(stru
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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