Re: [PATCH v10 36/38] x86/fred: Add fred_syscall_init()

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

On Wed, Sep 13 2023 at 21:48, Xin Li wrote:
> +static inline void fred_syscall_init(void)
> +{
> +     /*
> +      * Per FRED spec 5.0, FRED uses the ring 3 FRED entrypoint for SYSCALL
> +      * and SYSENTER, and ERETU is the only legit instruction to return to
> +      * ring 3, as a result there is _no_ need to setup the SYSCALL and
> +      * SYSENTER MSRs.
> +      *
> +      * Note, both sysexit and sysret cause #UD when FRED is enabled.
> +      */
> +     wrmsrl(MSR_LSTAR, 0ULL);
> +     wrmsrl_cstar(0ULL);

That write is pointless. See the comment in wrmsrl_cstar().

Thanks,

        tglx