Do atomic-AND to clear the dirty state of SPTEs. Optimize clear-dirty-log flow by avoiding to go through __handle_changed_spte() and directly call kvm_set_pfn_dirty() instead. Atomic-AND allows to fetch the latest value in SPTE, clear only its dirty state and set the new SPTE value. This optimization avoids executing unnecessary checks by not calling __handle_changed_spte(). With the removal of tdp_mmu_set_spte_no_dirty_log(), "record_dirty_log" parameter in __tdp_mmu_set_spte() is now obsolete. It will always be set to true by its caller. This dead code will be cleaned up in future commits. Tested on a VM (160 vCPUs, 160 GB memory) and found that performance of clear dirty log stage improved by ~40% in dirty_log_perf_test Before optimization: -------------------- Iteration 1 clear dirty log time: 3.638543593s Iteration 2 clear dirty log time: 3.145032742s Iteration 3 clear dirty log time: 3.142340358s Clear dirty log over 3 iterations took 9.925916693s. (Avg 3.308638897s/iteration) After optimization: ------------------- Iteration 1 clear dirty log time: 2.318988110s Iteration 2 clear dirty log time: 1.794470164s Iteration 3 clear dirty log time: 1.791668628s Clear dirty log over 3 iterations took 5.905126902s. (Avg 1.968375634s/iteration) Signed-off-by: Vipin Sharma <vipinsh@xxxxxxxxxx> --- arch/x86/kvm/mmu/tdp_iter.h | 14 ++++++++++++++ arch/x86/kvm/mmu/tdp_mmu.c | 35 +++++++++++++++-------------------- 2 files changed, 29 insertions(+), 20 deletions(-) diff --git a/arch/x86/kvm/mmu/tdp_iter.h b/arch/x86/kvm/mmu/tdp_iter.h index c11c5d00b2c1..fae559559a80 100644 --- a/arch/x86/kvm/mmu/tdp_iter.h +++ b/arch/x86/kvm/mmu/tdp_iter.h @@ -58,6 +58,20 @@ static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte, return old_spte; } +static inline u64 tdp_mmu_clear_spte_bits(tdp_ptep_t sptep, u64 old_spte, + u64 mask, int level) +{ + atomic64_t *sptep_atomic; + + if (kvm_tdp_mmu_spte_need_atomic_write(old_spte, level)) { + sptep_atomic = (atomic64_t *)rcu_dereference(sptep); + return (u64)atomic64_fetch_and(~mask, sptep_atomic); + } + + __kvm_tdp_mmu_write_spte(sptep, old_spte & ~mask); + return old_spte; +} + /* * A TDP iterator performs a pre-order walk over a TDP paging structure. */ diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index bba33aea0fb0..66ccbeb9d845 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -771,13 +771,6 @@ static inline void tdp_mmu_set_spte_no_acc_track(struct kvm *kvm, _tdp_mmu_set_spte(kvm, iter, new_spte, false, true); } -static inline void tdp_mmu_set_spte_no_dirty_log(struct kvm *kvm, - struct tdp_iter *iter, - u64 new_spte) -{ - _tdp_mmu_set_spte(kvm, iter, new_spte, true, false); -} - #define tdp_root_for_each_pte(_iter, _root, _start, _end) \ for_each_tdp_pte(_iter, _root, _start, _end) @@ -1677,8 +1670,13 @@ bool kvm_tdp_mmu_clear_dirty_slot(struct kvm *kvm, static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root, gfn_t gfn, unsigned long mask, bool wrprot) { + /* + * Either all SPTEs in TDP MMU will need write protection or none. This + * contract will not be modified for TDP MMU pages. + */ + u64 clear_bit = (wrprot || !kvm_ad_enabled()) ? PT_WRITABLE_MASK : + shadow_dirty_mask; struct tdp_iter iter; - u64 new_spte; rcu_read_lock(); @@ -1693,19 +1691,16 @@ static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root, mask &= ~(1UL << (iter.gfn - gfn)); - if (wrprot || spte_ad_need_write_protect(iter.old_spte)) { - if (is_writable_pte(iter.old_spte)) - new_spte = iter.old_spte & ~PT_WRITABLE_MASK; - else - continue; - } else { - if (iter.old_spte & shadow_dirty_mask) - new_spte = iter.old_spte & ~shadow_dirty_mask; - else - continue; - } + if (!(iter.old_spte & clear_bit)) + continue; - tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte); + iter.old_spte = tdp_mmu_clear_spte_bits(iter.sptep, + iter.old_spte, + clear_bit, iter.level); + trace_kvm_tdp_mmu_spte_changed(iter.as_id, iter.gfn, iter.level, + iter.old_spte, + iter.old_spte & ~clear_bit); + kvm_set_pfn_dirty(spte_to_pfn(iter.old_spte)); } rcu_read_unlock(); -- 2.39.1.581.gbfd45094c4-goog