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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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