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

Thomas Gleixner
2023-09-19T08:29:09Z

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