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Hello, Following my discussion with Andi. Here is a patch that introduces two new TIF flags to simplify the context switch code in __switch_to(). The idea is to minimize the number of cache lines accessed in the common case, i.e., when neither the debug registers nor the I/O bitmap are used. This patch covers the x86-64 modifications. A patch for i386 follows. Changelog: - add TIF_DEBUG to track when debug registers are active - add TIF_IO_BITMAP to track when I/O bitmap is used - modify __switch_to() to use the new TIF flags <signed-off-by>: eranian@hpl.hp.com Signed-off-by: Andi Kleen <ak@suse.de>
120 lines
3.0 KiB
C
120 lines
3.0 KiB
C
/*
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* linux/arch/x86_64/kernel/ioport.c
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*
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* This contains the io-permission bitmap code - written by obz, with changes
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* by Linus.
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*/
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#include <linux/sched.h>
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#include <linux/kernel.h>
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#include <linux/capability.h>
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#include <linux/errno.h>
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#include <linux/types.h>
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#include <linux/ioport.h>
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#include <linux/smp.h>
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#include <linux/smp_lock.h>
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#include <linux/stddef.h>
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#include <linux/slab.h>
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#include <linux/thread_info.h>
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/* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
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static void set_bitmap(unsigned long *bitmap, unsigned int base, unsigned int extent, int new_value)
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{
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int i;
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if (new_value)
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for (i = base; i < base + extent; i++)
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__set_bit(i, bitmap);
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else
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for (i = base; i < base + extent; i++)
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clear_bit(i, bitmap);
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}
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/*
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* this changes the io permissions bitmap in the current task.
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*/
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asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
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{
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unsigned int i, max_long, bytes, bytes_updated;
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struct thread_struct * t = ¤t->thread;
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struct tss_struct * tss;
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unsigned long *bitmap;
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if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
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return -EINVAL;
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if (turn_on && !capable(CAP_SYS_RAWIO))
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return -EPERM;
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/*
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* If it's the first ioperm() call in this thread's lifetime, set the
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* IO bitmap up. ioperm() is much less timing critical than clone(),
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* this is why we delay this operation until now:
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*/
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if (!t->io_bitmap_ptr) {
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bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
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if (!bitmap)
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return -ENOMEM;
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memset(bitmap, 0xff, IO_BITMAP_BYTES);
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t->io_bitmap_ptr = bitmap;
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set_thread_flag(TIF_IO_BITMAP);
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}
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/*
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* do it in the per-thread copy and in the TSS ...
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*
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* Disable preemption via get_cpu() - we must not switch away
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* because the ->io_bitmap_max value must match the bitmap
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* contents:
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*/
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tss = &per_cpu(init_tss, get_cpu());
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set_bitmap(t->io_bitmap_ptr, from, num, !turn_on);
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/*
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* Search for a (possibly new) maximum. This is simple and stupid,
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* to keep it obviously correct:
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*/
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max_long = 0;
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for (i = 0; i < IO_BITMAP_LONGS; i++)
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if (t->io_bitmap_ptr[i] != ~0UL)
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max_long = i;
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bytes = (max_long + 1) * sizeof(long);
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bytes_updated = max(bytes, t->io_bitmap_max);
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t->io_bitmap_max = bytes;
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/* Update the TSS: */
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memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
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put_cpu();
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return 0;
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}
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/*
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* sys_iopl has to be used when you want to access the IO ports
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* beyond the 0x3ff range: to get the full 65536 ports bitmapped
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* you'd need 8kB of bitmaps/process, which is a bit excessive.
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*
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* Here we just change the eflags value on the stack: we allow
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* only the super-user to do it. This depends on the stack-layout
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* on system-call entry - see also fork() and the signal handling
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* code.
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*/
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asmlinkage long sys_iopl(unsigned int level, struct pt_regs *regs)
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{
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unsigned int old = (regs->eflags >> 12) & 3;
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if (level > 3)
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return -EINVAL;
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/* Trying to gain more privileges? */
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if (level > old) {
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if (!capable(CAP_SYS_RAWIO))
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return -EPERM;
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}
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regs->eflags = (regs->eflags &~ 0x3000UL) | (level << 12);
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return 0;
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}
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