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Subject[patch V2 08/16] 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 along with the actual struct pointer
with the one which was last loaded on a CPU. Only update the bitmap if
either of the two changes. That should further reduce the overhead of I/O
bitmap scheduling when there are only a few I/O bitmap users on the system.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V2: New patch
---
arch/x86/include/asm/iobitmap.h | 1
arch/x86/include/asm/processor.h | 8 +++++++
arch/x86/kernel/cpu/common.c | 1
arch/x86/kernel/ioport.c | 9 +++++---
arch/x86/kernel/process.c | 40 +++++++++++++++++++++++++++++----------
5 files changed, 46 insertions(+), 13 deletions(-)

--- a/arch/x86/include/asm/iobitmap.h
+++ b/arch/x86/include/asm/iobitmap.h
@@ -5,6 +5,7 @@
#include <asm/processor.h>

struct io_bitmap {
+ u64 sequence;
unsigned int io_bitmap_max;
union {
unsigned long bits[IO_BITMAP_LONGS];
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -366,6 +366,14 @@ struct tss_struct {
struct x86_hw_tss x86_tss;

/*
+ * The bitmap pointer and the sequence number of the last active
+ * bitmap. last_bitmap cannot be dereferenced. It's solely for
+ * comparison.
+ */
+ struct io_bitmap *last_bitmap;
+ u64 last_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
* bitmap user will just set x86_tss.io_bitmap_base to a value
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1861,6 +1861,7 @@ void cpu_init(void)
/* Initialize the TSS. */
tss_setup_ist(tss);
tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;
+ tss->last_bitmap = NULL;
tss->io_bitmap_prev_max = 0;
memset(tss->io_bitmap_bytes, 0xff, sizeof(tss->io_bitmap_bytes));
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/iobitmap.h>
#include <asm/desc.h>

+static atomic64_t io_bitmap_sequence;
+
/*
* this changes the io permissions bitmap in the current task.
*/
@@ -76,14 +78,15 @@ long ksys_ioperm(unsigned long from, uns

iobm->io_bitmap_max = bytes;

- /* Update the TSS: */
- memcpy(tss->io_bitmap_bytes, iobm->bitmap_bytes, bytes_updated);
-
+ /* Update the sequence number to force an update in switch_to() */
+ iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);
/* Set the tasks io_bitmap pointer (might be the same) */
t->io_bitmap = iobm;
/* Mark it active for context switching */
set_thread_flag(TIF_IO_BITMAP);

+ /* Update the TSS: */
+ memcpy(tss->io_bitmap_bytes, iobm->bitmap_bytes, bytes_updated);
/* Make the bitmap base in the TSS valid */
tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;

--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -354,6 +354,29 @@ 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_bytes, iobm->bitmap_bytes,
+ max(tss->io_bitmap_prev_max, iobm->io_bitmap_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->io_bitmap_max;
+ tss->last_sequence = iobm->sequence;
+ tss->last_bitmap = iobm;
+}
+
static inline void switch_to_bitmap(struct thread_struct *next,
unsigned long tifp, unsigned long tifn)
{
@@ -363,18 +386,15 @@ 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 bitmap or the sequence
+ * number differs. The update time is accounted to the
+ * incoming task.
*/
- memcpy(tss->io_bitmap_bytes, iobm->bitmap_bytes,
- max(tss->io_bitmap_prev_max, iobm->io_bitmap_max));
+ if (tss->last_bitmap != iobm ||
+ tss->last_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 = iobm->io_bitmap_max;
+ /* Enable the bitmap */
tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;

/*

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