On Mon, 2023-06-19 at 17:46 +0300, kirill.shutemov@xxxxxxxxxxxxxxx wrote: > On Mon, Jun 19, 2023 at 07:31:21AM -0700, Dave Hansen wrote: > > On 6/19/23 04:43, Huang, Kai wrote: > > > On Mon, 2023-06-12 at 06:47 -0700, Dave Hansen wrote: > > > > On 6/12/23 03:27, Huang, Kai wrote: > > > > > So I think a __mb() after setting tdmr->pamt_4k_base should be good enough, as > > > > > it guarantees when setting to any pamt_*_size happens, the valid pamt_4k_base > > > > > will be seen by other cpus. > > > > > > > > > > Does it make sense? > > > > Just use a normal old atomic_t or set_bit()/test_bit(). They have > > > > built-in memory barriers are are less likely to get botched. > > > Hi Dave, > > > > > > Using atomic_set() requires changing tdmr->pamt_4k_base to atomic_t, which is a > > > little bit silly or overkill IMHO. Looking at the code, it seems > > > arch_atomic_set() simply uses __WRITE_ONCE(): > > > > How about _adding_ a variable that protects tdmr->pamt_4k_base? > > Wouldn't that be more straightforward than mucking around with existing > > types? > > What's wrong with simple global spinlock that protects all tdmr->pamt_*? > It is much easier to follow than a custom serialization scheme. > For this patch I think it's overkill to use spinlock because when the rebooting cpu is reading this all other cpus have been stopped already, so there's no concurrent thing here. However I just recall that the next #MC handler patch can also take advantage of this too because #MC handler can truly run concurrently with module initialization. Currently that one reads tdx_module_status first but again we may have the same memory order issue. So having a spinlock makes sense from #MC handler patch's point of view. I'll change to use spinlock if Dave is fine? Thanks for feedback!
