On Mon, Apr 06, 2020 at 08:10:29PM +0300, Jarkko Sakkinen wrote: > On Mon, Apr 06, 2020 at 07:36:38AM -0700, Sean Christopherson wrote: > > On Sat, Apr 04, 2020 at 04:12:02AM +0300, Jarkko Sakkinen wrote: > > > On Fri, Apr 03, 2020 at 04:42:39PM -0700, Sean Christopherson wrote: > > > > On Fri, Apr 03, 2020 at 12:35:50PM +0300, Jarkko Sakkinen wrote: > > > > > From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> > > > > > @@ -221,12 +224,16 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm) > > > > > return ret; > > > > > } > > > > > > > > > > + /* > > > > > + * The page reclaimer uses list version for synchronization instead of > > > > > + * synchronize_scru() because otherwise we could conflict with > > > > > + * dup_mmap(). > > > > > + */ > > > > > spin_lock(&encl->mm_lock); > > > > > list_add_rcu(&encl_mm->list, &encl->mm_list); > > > > > > > > You dropped the smp_wmb(). > > > > > > As I said to you in my review x86 pipeline does not reorder writes. > > > > And as I pointed out in this thread, smp_wmb() is a _compiler_ barrier if > > and only if CONFIG_SMP=y. The compiler can reorder list_add_rcu() and > > mm_list_version++ because from it's perspective there is no dependency > > between the two. And that's entirely true except for the SMP case where > > the consumer of mm_list_version is relying on the list to be updated before > > the version changes. > > I see. > > So why not change the variable volatile given that x86 is the only > arch that this code gets used? Please note that I'm fully aware of https://www.kernel.org/doc/html/latest/process/volatile-considered-harmful.html Just wondering. Anyway, I'll add smp_wmb() back since it is safe play in terms of acceptance. /Jarkko
