Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage further

Ingo Molnar
2019-11-07T07:37:25Z

* Thomas Gleixner <tglx@linutronix.de> wrote:

> @@ -365,19 +365,19 @@ 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.
> + * Store the dirty byte range of the last io bitmap offender. The
> + * next one will have to do the cleanup because the switch out to a
> + * non I/O bitmap user will just set x86_tss.io_bitmap_base to a
> + * value outside of the TSS limit to not penalize tasks which do
> + * not use the I/O bitmap at all.
> */
> - unsigned int io_bitmap_prev_max;
> + unsigned int io_zerobits_start;
> + unsigned int io_zerobits_end;
>
> /*
> - * The extra 1 is there because the CPU will access an
> - * additional byte beyond the end of the IO permission
> - * bitmap. The extra byte must be all 1 bits, and must
> - * be within the limit.
> + * The extra 1 is there because the CPU will access an additional
> + * byte beyond the end of the I/O permission bitmap. The extra byte
> + * must have all bits set and must be within the TSS limit.
> */
> unsigned long io_bitmap[IO_BITMAP_LONGS + 1];
> } __aligned(PAGE_SIZE);

Note that on 32-bit kernels this blows up our CPU area calculations:

./include/linux/compiler.h:350:38: error: call to ‘__compiletime_assert_181’ declared with attribute error: BUILD_BUG_ON failed: CPU_ENTRY_AREA_PAGES * PAGE_SIZE < CPU_ENTRY_AREA_MAP_SIZE
./include/linux/compiler.h:331:4: note: in definition of macro ‘__compiletime_assert’
./include/linux/compiler.h:350:2: note: in expansion of macro ‘_compiletime_assert’
./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
./include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
arch/x86/mm/cpu_entry_area.c:181:2: note: in expansion of macro ‘BUILD_BUG_ON’
make[2]: *** [scripts/Makefile.build:265: arch/x86/mm/cpu_entry_area.o] Error 1

Thanks,

Ingo