Re: [PATCH v5 25/34] x86/fred: disallow the swapgs instruction when FRED is enabled

[Peter Zijlstra]

On Mon, Mar 06, 2023 at 06:39:37PM -0800, Xin Li wrote:
> From: "H. Peter Anvin (Intel)" <hpa@xxxxxxxxx>
> 
> The FRED architecture establishes the full supervisor/user through:
> 1) FRED event delivery swaps the value of the GS base address and
>    that of the IA32_KERNEL_GS_BASE MSR.
> 2) ERETU swaps the value of the GS base address and that of the
>    IA32_KERNEL_GS_BASE MSR.
> Thus, the swapgs instruction is disallowed when FRED is enabled,
> otherwise it cauess #UD.
                 ^^^ --- new word :-)