Messages in this thread Patch in this message | | | Date | Mon, 11 Nov 2019 23:03:22 +0100 | From | Thomas Gleixner <> | Subject | [patch V2 08/16] 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 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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