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SubjectRe: [patch V2 14/16] x86/iopl: Restrict iopl() permission scope
On Mon, Nov 11, 2019 at 2:35 PM Thomas Gleixner <> wrote:
> From: Thomas Gleixner <>
> The access to the full I/O port range can be also provided by the TSS I/O
> bitmap, but that would require to copy 8k of data on scheduling in the
> task. As shown with the sched out optimization TSS.io_bitmap_base can be
> used to switch the incoming task to a preallocated I/O bitmap which has all
> bits zero, i.e. allows access to all I/O ports.
> Implementing this allows to provide an iopl() emulation mode which restricts
> the IOPL level 3 permissions to I/O port access but removes the STI/CLI
> permission which is coming with the hardware IOPL mechansim.
> Provide a config option to switch IOPL to emulation mode, make it the
> default and while at it also provide an option to disable IOPL completely.

Acked-by: Andy Lutomirski <>

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