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

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Date:   Thu, 7 Nov 2019 10:09:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Stephen Hemminger <stephen@...workplumber.org>,
        Willy Tarreau <w@....eu>, Juergen Gross <jgross@...e.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [patch 7/9] x86/iopl: Restrict iopl() permission scope

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.