x86/io: Speedup schedule out of I/O bitmap user

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There is no requirement to update the TSS I/O bitmap when a thread using it is
scheduled out and the incoming thread does not use it.

For the permission check based on the TSS I/O bitmap the CPU calculates the memory
location of the I/O bitmap by the address of the TSS and the io_bitmap_base member
of the tss_struct. The easiest way to invalidate the I/O bitmap is to switch the
offset to an address outside of the TSS limit.

If an I/O instruction is issued from user space the TSS limit causes #GP to be
raised in the same was as valid I/O bitmap with all bits set to 1 would do.

This removes the extra work when an I/O bitmap using task is scheduled out
and puts the burden on the rare I/O bitmap users when they are scheduled
in.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

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This commit is contained in:

Thomas Gleixner 2019-11-11 23:03:20 +01:00

parent 32f3bf67ee

commit ecc7e37d4d

5 changed files with 69 additions and 41 deletions

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38

arch/x86/include/asm/processor.h

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3

arch/x86/kernel/cpu/common.c

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2

arch/x86/kernel/doublefault.c

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4

arch/x86/kernel/ioport.c

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63

arch/x86/kernel/process.c

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