From ae31cea86ab31f3d2e15d6cc8710754ad7330c9e Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 12 Nov 2019 19:05:31 +0100 Subject: x86/ioperm: Simplify first ioperm() invocation logic On the first allocation of a task the I/O bitmap needs to be allocated. After the allocation it is installed as an empty bitmap and immediately afterwards updated. Avoid that and just do the initial updates (store bitmap pointer, set TIF flag and make TSS limit valid) in the update path unconditionally. If the bitmap was already active this is redundant but harmless. Preparatory change for later optimizations in the context switch code. Signed-off-by: Thomas Gleixner --- arch/x86/kernel/ioport.c | 55 +++++++++++++++++++++++------------------------- 1 file changed, 26 insertions(+), 29 deletions(-) (limited to 'arch/x86/kernel/ioport.c') diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c index 76fc2efa05d5..ca6aa1e33c97 100644 --- a/arch/x86/kernel/ioport.c +++ b/arch/x86/kernel/ioport.c @@ -18,9 +18,10 @@ */ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on) { + unsigned int i, max_long, bytes, bytes_updated; struct thread_struct *t = ¤t->thread; struct tss_struct *tss; - unsigned int i, max_long, bytes, bytes_updated; + unsigned long *bitmap; if ((from + num <= from) || (from + num > IO_BITMAP_BITS)) return -EINVAL; @@ -33,59 +34,55 @@ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on) * IO bitmap up. ioperm() is much less timing critical than clone(), * this is why we delay this operation until now: */ - if (!t->io_bitmap_ptr) { - unsigned long *bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL); - + bitmap = t->io_bitmap_ptr; + if (!bitmap) { + bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL); if (!bitmap) return -ENOMEM; memset(bitmap, 0xff, IO_BITMAP_BYTES); - t->io_bitmap_ptr = bitmap; - set_thread_flag(TIF_IO_BITMAP); - - /* - * Now that we have an IO bitmap, we need our TSS limit to be - * correct. It's fine if we are preempted after doing this: - * with TIF_IO_BITMAP set, context switches will keep our TSS - * limit correct. - */ - preempt_disable(); - refresh_tss_limit(); - preempt_enable(); } /* - * do it in the per-thread copy and in the TSS ... - * - * Disable preemption via get_cpu() - we must not switch away - * because the ->io_bitmap_max value must match the bitmap - * contents: + * Update the bitmap and the TSS copy with preemption disabled to + * prevent a race against context switch. */ - tss = &per_cpu(cpu_tss_rw, get_cpu()); - + preempt_disable(); if (turn_on) - bitmap_clear(t->io_bitmap_ptr, from, num); + bitmap_clear(bitmap, from, num); else - bitmap_set(t->io_bitmap_ptr, from, num); + bitmap_set(bitmap, from, num); /* * Search for a (possibly new) maximum. This is simple and stupid, * to keep it obviously correct: */ max_long = 0; - for (i = 0; i < IO_BITMAP_LONGS; i++) - if (t->io_bitmap_ptr[i] != ~0UL) + for (i = 0; i < IO_BITMAP_LONGS; i++) { + if (bitmap[i] != ~0UL) max_long = i; + } bytes = (max_long + 1) * sizeof(unsigned long); bytes_updated = max(bytes, t->io_bitmap_max); + /* Update the thread data */ t->io_bitmap_max = bytes; + /* + * 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 + * invocation. + */ + t->io_bitmap_ptr = bitmap; + set_thread_flag(TIF_IO_BITMAP); - /* Update the TSS: */ + /* Update the TSS */ + tss = this_cpu_ptr(&cpu_tss_rw); memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated); + /* Make sure the TSS limit covers the I/O bitmap. */ + refresh_tss_limit(); - put_cpu(); + preempt_enable(); return 0; } -- cgit v1.2.3