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When mmu_lock is held, it should be impossible for a different task to zap a SPTE, _and_ zapped SPTEs must be removed from their rmap chain prior to dropping mmu_lock. Thus, the normal walker BUG()s if a non-present SPTE is encountered as something is wildly broken. When walking rmaps without holding mmu_lock, the SPTEs pointed at by the rmap chain can be zapped/dropped, and so a lockless walk can observe a non-present SPTE if it runs concurrently with a different operation that is zapping SPTEs. Signed-off-by: Sean Christopherson Signed-off-by: James Houghton --- arch/x86/kvm/mmu/mmu.c | 75 +++++++++++++++++++++++------------------- 1 file changed, 42 insertions(+), 33 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 1cdb77df0a4d..71019762a28a 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -870,7 +870,7 @@ static struct kvm_memory_slot *gfn_to_memslot_dirty_bitmap(struct kvm_vcpu *vcpu */ #define KVM_RMAP_LOCKED BIT(1) -static unsigned long kvm_rmap_lock(struct kvm_rmap_head *rmap_head) +static unsigned long __kvm_rmap_lock(struct kvm_rmap_head *rmap_head) { unsigned long old_val, new_val; @@ -914,14 +914,25 @@ static unsigned long kvm_rmap_lock(struct kvm_rmap_head *rmap_head) */ } while (!atomic_long_try_cmpxchg_acquire(&rmap_head->val, &old_val, new_val)); - /* Return the old value, i.e. _without_ the LOCKED bit set. */ + /* + * Return the old value, i.e. _without_ the LOCKED bit set. It's + * impossible for the return value to be 0 (see above), i.e. the read- + * only unlock flow can't get a false positive and fail to unlock. + */ return old_val; } +static unsigned long kvm_rmap_lock(struct kvm *kvm, + struct kvm_rmap_head *rmap_head) +{ + lockdep_assert_held_write(&kvm->mmu_lock); + return __kvm_rmap_lock(rmap_head); +} + static void kvm_rmap_unlock(struct kvm_rmap_head *rmap_head, unsigned long new_val) { - WARN_ON_ONCE(new_val & KVM_RMAP_LOCKED); + KVM_MMU_WARN_ON(new_val & KVM_RMAP_LOCKED); /* * Ensure that all accesses to the rmap have completed * before we actually unlock the rmap. @@ -961,14 +972,14 @@ static void kvm_rmap_unlock_readonly(struct kvm_rmap_head *rmap_head, /* * Returns the number of pointers in the rmap chain, not counting the new one. */ -static int pte_list_add(struct kvm_mmu_memory_cache *cache, u64 *spte, - struct kvm_rmap_head *rmap_head) +static int pte_list_add(struct kvm *kvm, struct kvm_mmu_memory_cache *cache, + u64 *spte, struct kvm_rmap_head *rmap_head) { unsigned long old_val, new_val; struct pte_list_desc *desc; int count = 0; - old_val = kvm_rmap_lock(rmap_head); + old_val = kvm_rmap_lock(kvm, rmap_head); if (!old_val) { new_val = (unsigned long)spte; @@ -1048,7 +1059,7 @@ static void pte_list_remove(struct kvm *kvm, u64 *spte, unsigned long rmap_val; int i; - rmap_val = kvm_rmap_lock(rmap_head); + rmap_val = kvm_rmap_lock(kvm, rmap_head); if (KVM_BUG_ON_DATA_CORRUPTION(!rmap_val, kvm)) goto out; @@ -1092,7 +1103,7 @@ static bool kvm_zap_all_rmap_sptes(struct kvm *kvm, unsigned long rmap_val; int i; - rmap_val = kvm_rmap_lock(rmap_head); + rmap_val = kvm_rmap_lock(kvm, rmap_head); if (!rmap_val) return false; @@ -1184,23 +1195,18 @@ static u64 *rmap_get_first(struct kvm_rmap_head *rmap_head, struct rmap_iterator *iter) { unsigned long rmap_val = kvm_rmap_get(rmap_head); - u64 *sptep; if (!rmap_val) return NULL; if (!(rmap_val & KVM_RMAP_MANY)) { iter->desc = NULL; - sptep = (u64 *)rmap_val; - goto out; + return (u64 *)rmap_val; } iter->desc = (struct pte_list_desc *)(rmap_val & ~KVM_RMAP_MANY); iter->pos = 0; - sptep = iter->desc->sptes[iter->pos]; -out: - BUG_ON(!is_shadow_present_pte(*sptep)); - return sptep; + return iter->desc->sptes[iter->pos]; } /* @@ -1210,14 +1216,11 @@ static u64 *rmap_get_first(struct kvm_rmap_head *rmap_head, */ static u64 *rmap_get_next(struct rmap_iterator *iter) { - u64 *sptep; - if (iter->desc) { if (iter->pos < PTE_LIST_EXT - 1) { ++iter->pos; - sptep = iter->desc->sptes[iter->pos]; - if (sptep) - goto out; + if (iter->desc->sptes[iter->pos]) + return iter->desc->sptes[iter->pos]; } iter->desc = iter->desc->more; @@ -1225,20 +1228,24 @@ static u64 *rmap_get_next(struct rmap_iterator *iter) if (iter->desc) { iter->pos = 0; /* desc->sptes[0] cannot be NULL */ - sptep = iter->desc->sptes[iter->pos]; - goto out; + return iter->desc->sptes[iter->pos]; } } return NULL; -out: - BUG_ON(!is_shadow_present_pte(*sptep)); - return sptep; } -#define for_each_rmap_spte(_rmap_head_, _iter_, _spte_) \ - for (_spte_ = rmap_get_first(_rmap_head_, _iter_); \ - _spte_; _spte_ = rmap_get_next(_iter_)) +#define __for_each_rmap_spte(_rmap_head_, _iter_, _sptep_) \ + for (_sptep_ = rmap_get_first(_rmap_head_, _iter_); \ + _sptep_; _sptep_ = rmap_get_next(_iter_)) + +#define for_each_rmap_spte(_rmap_head_, _iter_, _sptep_) \ + __for_each_rmap_spte(_rmap_head_, _iter_, _sptep_) \ + if (!WARN_ON_ONCE(!is_shadow_present_pte(*(_sptep_)))) \ + +#define for_each_rmap_spte_lockless(_rmap_head_, _iter_, _sptep_, _spte_) \ + __for_each_rmap_spte(_rmap_head_, _iter_, _sptep_) \ + if (is_shadow_present_pte(_spte_ = mmu_spte_get_lockless(sptep))) static void drop_spte(struct kvm *kvm, u64 *sptep) { @@ -1324,12 +1331,13 @@ static bool __rmap_clear_dirty(struct kvm *kvm, struct kvm_rmap_head *rmap_head, struct rmap_iterator iter; bool flush = false; - for_each_rmap_spte(rmap_head, &iter, sptep) + for_each_rmap_spte(rmap_head, &iter, sptep) { if (spte_ad_need_write_protect(*sptep)) flush |= test_and_clear_bit(PT_WRITABLE_SHIFT, (unsigned long *)sptep); else flush |= spte_clear_dirty(sptep); + } return flush; } @@ -1650,7 +1658,7 @@ static void __rmap_add(struct kvm *kvm, kvm_update_page_stats(kvm, sp->role.level, 1); rmap_head = gfn_to_rmap(gfn, sp->role.level, slot); - rmap_count = pte_list_add(cache, spte, rmap_head); + rmap_count = pte_list_add(kvm, cache, spte, rmap_head); if (rmap_count > kvm->stat.max_mmu_rmap_size) kvm->stat.max_mmu_rmap_size = rmap_count; @@ -1796,13 +1804,14 @@ static unsigned kvm_page_table_hashfn(gfn_t gfn) return hash_64(gfn, KVM_MMU_HASH_SHIFT); } -static void mmu_page_add_parent_pte(struct kvm_mmu_memory_cache *cache, +static void mmu_page_add_parent_pte(struct kvm *kvm, + struct kvm_mmu_memory_cache *cache, struct kvm_mmu_page *sp, u64 *parent_pte) { if (!parent_pte) return; - pte_list_add(cache, parent_pte, &sp->parent_ptes); + pte_list_add(kvm, cache, parent_pte, &sp->parent_ptes); } static void mmu_page_remove_parent_pte(struct kvm *kvm, struct kvm_mmu_page *sp, @@ -2492,7 +2501,7 @@ static void __link_shadow_page(struct kvm *kvm, mmu_spte_set(sptep, spte); - mmu_page_add_parent_pte(cache, sp, sptep); + mmu_page_add_parent_pte(kvm, cache, sp, sptep); /* * The non-direct sub-pagetable must be updated before linking. For