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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>
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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@@ -330,8 +330,23 @@ struct x86_hw_tss {
#define IO_BITMAP_BITS 65536
#define IO_BITMAP_BYTES (IO_BITMAP_BITS/8)
#define IO_BITMAP_LONGS (IO_BITMAP_BYTES/sizeof(long))
#define IO_BITMAP_OFFSET (offsetof(struct tss_struct, io_bitmap) - offsetof(struct tss_struct, x86_tss))
#define INVALID_IO_BITMAP_OFFSET 0x8000
#define IO_BITMAP_OFFSET_VALID \
(offsetof(struct tss_struct, io_bitmap) - \
offsetof(struct tss_struct, x86_tss))
/*
* sizeof(unsigned long) coming from an extra "long" at the end
* of the iobitmap.
*
* -1? seg base+limit should be pointing to the address of the
* last valid byte
*/
#define __KERNEL_TSS_LIMIT \
(IO_BITMAP_OFFSET_VALID + IO_BITMAP_BYTES + sizeof(unsigned long) - 1)
/* Base offset outside of TSS_LIMIT so unpriviledged IO causes #GP */
#define IO_BITMAP_OFFSET_INVALID (__KERNEL_TSS_LIMIT + 1)
struct entry_stack {
unsigned long words[64];
@@ -349,6 +364,15 @@ struct tss_struct {
*/
struct x86_hw_tss x86_tss;
/*
* 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
* outside of the TSS limit. So for sane tasks there is no need to
* actually touch the io_bitmap at all.
*/
unsigned int io_bitmap_prev_max;
/*
* The extra 1 is there because the CPU will access an
* additional byte beyond the end of the IO permission
@@ -360,16 +384,6 @@ struct tss_struct {
DECLARE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss_rw);
/*
* sizeof(unsigned long) coming from an extra "long" at the end
* of the iobitmap.
*
* -1? seg base+limit should be pointing to the address of the
* last valid byte
*/
#define __KERNEL_TSS_LIMIT \
(IO_BITMAP_OFFSET + IO_BITMAP_BYTES + sizeof(unsigned long) - 1)
/* Per CPU interrupt stacks */
struct irq_stack {
char stack[IRQ_STACK_SIZE];