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

[Thomas Gleixner]

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