Walk the TDP MMU in an RCU read-side critical section. This requires a way to do RCU-safe walking of the tdp_mmu_roots; do this with a new macro. The PTE modifications are now done atomically, and kvm_tdp_mmu_spte_need_atomic_write() has been updated to account for the fact that kvm_age_gfn can now lockless update the accessed bit and the R/X bits).
If the cmpxchg for marking the spte for access tracking fails, we simply retry if the spte is still a leaf PTE. If it isn't, we return false to continue the walk.
Harvesting age information from the shadow MMU is still done while holding the MMU write lock.
Suggested-by: Yu Zhao yuzhao@google.com Signed-off-by: James Houghton jthoughton@google.com --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/mmu/mmu.c | 18 ++++----- arch/x86/kvm/mmu/tdp_iter.h | 27 +++++++------ arch/x86/kvm/mmu/tdp_mmu.c | 67 +++++++++++++++++++++++++-------- 4 files changed, 76 insertions(+), 37 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index ece45b3f6f20..48fb29bb782f 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1438,6 +1438,7 @@ struct kvm_arch { * tdp_mmu_page set. * * For reads, this list is protected by: + * RCU alone or * the MMU lock in read mode + RCU or * the MMU lock in write mode * diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 6a2a557c2c31..956834da8a0e 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -1630,16 +1630,15 @@ bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) { bool young = false;
- write_lock(&kvm->mmu_lock); - - if (kvm_memslots_have_rmaps(kvm)) + if (kvm_memslots_have_rmaps(kvm)) { + write_lock(&kvm->mmu_lock); young = kvm_handle_gfn_range(kvm, range, kvm_age_rmap); + write_unlock(&kvm->mmu_lock); + }
if (tdp_mmu_enabled) young |= kvm_tdp_mmu_age_gfn_range(kvm, range);
- write_unlock(&kvm->mmu_lock); - return young; }
@@ -1647,16 +1646,15 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) { bool young = false;
- write_lock(&kvm->mmu_lock); - - if (kvm_memslots_have_rmaps(kvm)) + if (kvm_memslots_have_rmaps(kvm)) { + write_lock(&kvm->mmu_lock); young = kvm_handle_gfn_range(kvm, range, kvm_test_age_rmap); + write_unlock(&kvm->mmu_lock); + }
if (tdp_mmu_enabled) young |= kvm_tdp_mmu_test_age_gfn(kvm, range);
- write_unlock(&kvm->mmu_lock); - return young; }
diff --git a/arch/x86/kvm/mmu/tdp_iter.h b/arch/x86/kvm/mmu/tdp_iter.h index fae559559a80..f558ae9054af 100644 --- a/arch/x86/kvm/mmu/tdp_iter.h +++ b/arch/x86/kvm/mmu/tdp_iter.h @@ -24,16 +24,24 @@ static inline u64 kvm_tdp_mmu_write_spte_atomic(tdp_ptep_t sptep, u64 new_spte) return xchg(rcu_dereference(sptep), new_spte); }
+static inline u64 tdp_mmu_clear_spte_bits_atomic(tdp_ptep_t sptep, u64 mask) +{ + atomic64_t *sptep_atomic = (atomic64_t *)rcu_dereference(sptep); + + return (u64)atomic64_fetch_and(~mask, sptep_atomic); +} + static inline void __kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 new_spte) { WRITE_ONCE(*rcu_dereference(sptep), new_spte); }
/* - * SPTEs must be modified atomically if they are shadow-present, leaf - * SPTEs, and have volatile bits, i.e. has bits that can be set outside - * of mmu_lock. The Writable bit can be set by KVM's fast page fault - * handler, and Accessed and Dirty bits can be set by the CPU. + * SPTEs must be modified atomically if they have bits that can be set outside + * of the mmu_lock. This can happen for any shadow-present leaf SPTEs, as the + * Writable bit can be set by KVM's fast page fault handler, the Accessed and + * Dirty bits can be set by the CPU, and the Accessed and R/X bits can be + * cleared by age_gfn_range. * * Note, non-leaf SPTEs do have Accessed bits and those bits are * technically volatile, but KVM doesn't consume the Accessed bit of @@ -44,8 +52,7 @@ static inline void __kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 new_spte) static inline bool kvm_tdp_mmu_spte_need_atomic_write(u64 old_spte, int level) { return is_shadow_present_pte(old_spte) && - is_last_spte(old_spte, level) && - spte_has_volatile_bits(old_spte); + is_last_spte(old_spte, level); }
static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte, @@ -61,12 +68,8 @@ static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 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); - } + if (kvm_tdp_mmu_spte_need_atomic_write(old_spte, level)) + return tdp_mmu_clear_spte_bits_atomic(sptep, mask);
__kvm_tdp_mmu_write_spte(sptep, old_spte & ~mask); return old_spte; diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 1259dd63defc..c74b0221dae0 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -29,6 +29,11 @@ static __always_inline bool kvm_lockdep_assert_mmu_lock_held(struct kvm *kvm,
return true; } +static __always_inline bool kvm_lockdep_assert_rcu_read_lock_held(void) +{ + WARN_ON_ONCE(!rcu_read_lock_held()); + return true; +}
void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm) { @@ -178,6 +183,15 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm, ((_only_valid) && (_root)->role.invalid))) { \ } else
+/* + * Iterate over all TDP MMU roots in an RCU read-side critical section. + */ +#define for_each_tdp_mmu_root_rcu(_kvm, _root, _as_id) \ + list_for_each_entry_rcu(_root, &_kvm->arch.tdp_mmu_roots, link) \ + if (kvm_lockdep_assert_rcu_read_lock_held() && \ + (_as_id >= 0 && kvm_mmu_page_as_id(_root) != _as_id)) { \ + } else + #define for_each_tdp_mmu_root(_kvm, _root, _as_id) \ __for_each_tdp_mmu_root(_kvm, _root, _as_id, false)
@@ -1223,6 +1237,27 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm, return ret; }
+static __always_inline bool kvm_tdp_mmu_handle_gfn_lockless( + struct kvm *kvm, + struct kvm_gfn_range *range, + tdp_handler_t handler) +{ + struct kvm_mmu_page *root; + struct tdp_iter iter; + bool ret = false; + + rcu_read_lock(); + + for_each_tdp_mmu_root_rcu(kvm, root, range->slot->as_id) { + tdp_root_for_each_leaf_pte(iter, root, range->start, range->end) + ret |= handler(kvm, &iter, range); + } + + rcu_read_unlock(); + + return ret; +} + /* * Mark the SPTEs range of GFNs [start, end) unaccessed and return non-zero * if any of the GFNs in the range have been accessed. @@ -1236,28 +1271,30 @@ 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; + /* Otherwise, continue walking. */ + return false; + } if (is_writable_pte(iter->old_spte)) kvm_set_pfn_dirty(spte_to_pfn(iter->old_spte)); - - new_spte = mark_spte_for_access_track(iter->old_spte); - iter->old_spte = kvm_tdp_mmu_write_spte(iter->sptep, - iter->old_spte, new_spte, - iter->level); }
trace_kvm_tdp_mmu_spte_changed(iter->as_id, iter->gfn, iter->level, @@ -1267,7 +1304,7 @@ static bool age_gfn_range(struct kvm *kvm, struct tdp_iter *iter,
bool kvm_tdp_mmu_age_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range) { - return kvm_tdp_mmu_handle_gfn(kvm, range, age_gfn_range); + return kvm_tdp_mmu_handle_gfn_lockless(kvm, range, age_gfn_range); }
static bool test_age_gfn(struct kvm *kvm, struct tdp_iter *iter, @@ -1278,7 +1315,7 @@ static bool test_age_gfn(struct kvm *kvm, struct tdp_iter *iter,
bool kvm_tdp_mmu_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) { - return kvm_tdp_mmu_handle_gfn(kvm, range, test_age_gfn); + return kvm_tdp_mmu_handle_gfn_lockless(kvm, range, test_age_gfn); }
/*