Re: [patch 7/9] x86/iopl: Restrict iopl() permission scope

[Peter Zijlstra]

On Wed, Nov 06, 2019 at 08:35:06PM +0100, Thomas Gleixner wrote:

Something like:

> @@ -379,7 +383,8 @@ struct tss_struct {
>  	 * 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];

#ifndef X86_IOPL_NONE
> +	unsigned long		io_bitmap_map[IO_BITMAP_LONGS + 1];
#ifdef X86_IOPL_EMLATION
> +	unsigned long		io_bitmap_all[IO_BITMAP_LONGS + 1];
#endif /* X86_IOPL_EMLATION */
#endif /* !X86_IOPL_NONE */

>  } __aligned(PAGE_SIZE);

Would allow us to reclaim those 8/16K bitmaps for LEGACY/NONE kernels.