On 6/28/23 02:20, Nikolay Borisov wrote: >> >> + /* >> + * Starting from this point the system may have TDX private >> + * memory. Make it globally visible so tdx_reset_memory() only >> + * reads TDMRs/PAMTs when they are stable. >> + * >> + * Note using atomic_inc_return() to provide the explicit memory >> + * ordering isn't mandatory here as the WBINVD above already >> + * does that. Compiler barrier isn't needed here either. >> + */ > > If it's not needed, then why use it? Simply do atomic_inc() and instead > rephrase the comment to state what are the ordering guarantees and how > they are achieved (i.e by using wbinvd above). Even better, explain why the barrier needs to be there and *IGNORE* the WBVIND. If the WBINVD gets moved -- or if the gods ever bless us with a halfway reasonable way to flush the caches that's not full serializing -- this code is screwed. There is _zero_ reason to try and "optimize" this junk by trying to get rid of a memory barrier at the risk of screwing it over later. I use "optimize" in quotes because that's a highly charitable way of describing this activity.
