On Thu, Aug 29, 2024, James Houghton wrote: > On Fri, Aug 16, 2024 at 6:05 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > > +static __always_inline bool kvm_tdp_mmu_handle_gfn_lockless( > > > + struct kvm *kvm, > > > + struct kvm_gfn_range *range, > > > + tdp_handler_t handler) > > > > Please burn all the Google3 from your brain, and code ;-) > > I indented this way to avoid going past the 80 character limit. I've > adjusted it to be more like the other functions in this file. > > Perhaps I should put `static __always_inline bool` on its own line? Noooo. Do not wrap before the function name. Linus has a nice explanation/rant on this[1]. In this case, I'm pretty sure you can avoid the helper and simply handle all aging paths in a single API, e.g. similar to what I proposed for the shadow MMU[2]. [1] https://lore.kernel.org/all/CAHk-=wjoLAYG446ZNHfg=GhjSY6nFmuB_wA8fYd5iLBNXjo9Bw@xxxxxxxxxxxxxx [2] https://lore.kernel.org/all/20240809194335.1726916-16-seanjc@xxxxxxxxxx > > > /* > > > * Mark the SPTEs range of GFNs [start, end) unaccessed and return non-zero > > > * if any of the GFNs in the range have been accessed. > > > @@ -1237,28 +1272,30 @@ static bool age_gfn_range(struct kvm *kvm, struct tdp_iter *iter, > > > { > > > u64 new_spte; > > > > > > +retry: > > > /* If we have a non-accessed entry we don't need to change the pte. */ > > > if (!is_accessed_spte(iter->old_spte)) > > > return false; > > > > > > if (spte_ad_enabled(iter->old_spte)) { > > > - iter->old_spte = tdp_mmu_clear_spte_bits(iter->sptep, > > > - iter->old_spte, > > > - shadow_accessed_mask, > > > - iter->level); > > > + iter->old_spte = tdp_mmu_clear_spte_bits_atomic(iter->sptep, > > > + shadow_accessed_mask); > > > new_spte = iter->old_spte & ~shadow_accessed_mask; > > > } else { > > > - /* > > > - * Capture the dirty status of the page, so that it doesn't get > > > - * lost when the SPTE is marked for access tracking. > > > - */ > > > + new_spte = mark_spte_for_access_track(iter->old_spte); > > > + if (__tdp_mmu_set_spte_atomic(iter, new_spte)) { > > > + /* > > > + * The cmpxchg failed. If the spte is still a > > > + * last-level spte, we can safely retry. > > > + */ > > > + if (is_shadow_present_pte(iter->old_spte) && > > > + is_last_spte(iter->old_spte, iter->level)) > > > + goto retry; > > > > Do we have a feel for how often conflicts actually happen? I.e. is it worth > > retrying and having to worry about infinite loops, however improbable they may > > be? > > I'm not sure how common this is. I think it's probably better not to > retry actually. If the cmpxchg fails, this spte is probably young > anyway, so I can just `return true` instead of potentially retrying. > This is all best-effort anyway. +1
