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

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Message-ID: <20230320165411.GT2194297@hirez.programming.kicks-ass.net>
Date:   Mon, 20 Mar 2023 17:54:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Xin Li <xin3.li@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        andrew.cooper3@...rix.com, seanjc@...gle.com, pbonzini@...hat.com,
        ravi.v.shankar@...el.com
Subject: Re: [PATCH v5 25/34] x86/fred: disallow the swapgs instruction when
 FRED is enabled

On Mon, Mar 06, 2023 at 06:39:37PM -0800, Xin Li wrote:
> From: "H. Peter Anvin (Intel)" <hpa@...or.com>
> 
> 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 :-)