diff options
Diffstat (limited to 'arch/x86/kvm/mmu/tdp_mmu.c')
| -rw-r--r-- | arch/x86/kvm/mmu/tdp_mmu.c | 82 |
1 files changed, 53 insertions, 29 deletions
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index edc68538819b..922b06bf4b94 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -426,9 +426,9 @@ static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared) tdp_mmu_unlink_sp(kvm, sp, shared); for (i = 0; i < PT64_ENT_PER_PAGE; i++) { - u64 *sptep = rcu_dereference(pt) + i; + tdp_ptep_t sptep = pt + i; gfn_t gfn = base_gfn + i * KVM_PAGES_PER_HPAGE(level); - u64 old_child_spte; + u64 old_spte; if (shared) { /* @@ -440,8 +440,8 @@ static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared) * value to the removed SPTE value. */ for (;;) { - old_child_spte = xchg(sptep, REMOVED_SPTE); - if (!is_removed_spte(old_child_spte)) + old_spte = kvm_tdp_mmu_write_spte_atomic(sptep, REMOVED_SPTE); + if (!is_removed_spte(old_spte)) break; cpu_relax(); } @@ -455,23 +455,43 @@ static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared) * are guarded by the memslots generation, not by being * unreachable. */ - old_child_spte = READ_ONCE(*sptep); - if (!is_shadow_present_pte(old_child_spte)) + old_spte = kvm_tdp_mmu_read_spte(sptep); + if (!is_shadow_present_pte(old_spte)) continue; /* - * Marking the SPTE as a removed SPTE is not - * strictly necessary here as the MMU lock will - * stop other threads from concurrently modifying - * this SPTE. Using the removed SPTE value keeps - * the two branches consistent and simplifies - * the function. + * Use the common helper instead of a raw WRITE_ONCE as + * the SPTE needs to be updated atomically if it can be + * modified by a different vCPU outside of mmu_lock. + * Even though the parent SPTE is !PRESENT, the TLB + * hasn't yet been flushed, and both Intel and AMD + * document that A/D assists can use upper-level PxE + * entries that are cached in the TLB, i.e. the CPU can + * still access the page and mark it dirty. + * + * No retry is needed in the atomic update path as the + * sole concern is dropping a Dirty bit, i.e. no other + * task can zap/remove the SPTE as mmu_lock is held for + * write. Marking the SPTE as a removed SPTE is not + * strictly necessary for the same reason, but using + * the remove SPTE value keeps the shared/exclusive + * paths consistent and allows the handle_changed_spte() + * call below to hardcode the new value to REMOVED_SPTE. + * + * Note, even though dropping a Dirty bit is the only + * scenario where a non-atomic update could result in a + * functional bug, simply checking the Dirty bit isn't + * sufficient as a fast page fault could read the upper + * level SPTE before it is zapped, and then make this + * target SPTE writable, resume the guest, and set the + * Dirty bit between reading the SPTE above and writing + * it here. */ - WRITE_ONCE(*sptep, REMOVED_SPTE); + old_spte = kvm_tdp_mmu_write_spte(sptep, old_spte, + REMOVED_SPTE, level); } handle_changed_spte(kvm, kvm_mmu_page_as_id(sp), gfn, - old_child_spte, REMOVED_SPTE, level, - shared); + old_spte, REMOVED_SPTE, level, shared); } call_rcu(&sp->rcu_head, tdp_mmu_free_sp_rcu_callback); @@ -667,14 +687,13 @@ static inline int tdp_mmu_zap_spte_atomic(struct kvm *kvm, KVM_PAGES_PER_HPAGE(iter->level)); /* - * No other thread can overwrite the removed SPTE as they - * must either wait on the MMU lock or use - * tdp_mmu_set_spte_atomic which will not overwrite the - * special removed SPTE value. No bookkeeping is needed - * here since the SPTE is going from non-present - * to non-present. + * No other thread can overwrite the removed SPTE as they must either + * wait on the MMU lock or use tdp_mmu_set_spte_atomic() which will not + * overwrite the special removed SPTE value. No bookkeeping is needed + * here since the SPTE is going from non-present to non-present. Use + * the raw write helper to avoid an unnecessary check on volatile bits. */ - kvm_tdp_mmu_write_spte(iter->sptep, 0); + __kvm_tdp_mmu_write_spte(iter->sptep, 0); return 0; } @@ -699,10 +718,13 @@ static inline int tdp_mmu_zap_spte_atomic(struct kvm *kvm, * unless performing certain dirty logging operations. * Leaving record_dirty_log unset in that case prevents page * writes from being double counted. + * + * Returns the old SPTE value, which _may_ be different than @old_spte if the + * SPTE had voldatile bits. */ -static void __tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep, - u64 old_spte, u64 new_spte, gfn_t gfn, int level, - bool record_acc_track, bool record_dirty_log) +static u64 __tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep, + u64 old_spte, u64 new_spte, gfn_t gfn, int level, + bool record_acc_track, bool record_dirty_log) { lockdep_assert_held_write(&kvm->mmu_lock); @@ -715,7 +737,7 @@ static void __tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep, */ WARN_ON(is_removed_spte(old_spte) || is_removed_spte(new_spte)); - kvm_tdp_mmu_write_spte(sptep, new_spte); + old_spte = kvm_tdp_mmu_write_spte(sptep, old_spte, new_spte, level); __handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level, false); @@ -724,6 +746,7 @@ static void __tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep, if (record_dirty_log) handle_changed_spte_dirty_log(kvm, as_id, gfn, old_spte, new_spte, level); + return old_spte; } static inline void _tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter, @@ -732,9 +755,10 @@ static inline void _tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter, { WARN_ON_ONCE(iter->yielded); - __tdp_mmu_set_spte(kvm, iter->as_id, iter->sptep, iter->old_spte, - new_spte, iter->gfn, iter->level, - record_acc_track, record_dirty_log); + iter->old_spte = __tdp_mmu_set_spte(kvm, iter->as_id, iter->sptep, + iter->old_spte, new_spte, + iter->gfn, iter->level, + record_acc_track, record_dirty_log); } static inline void tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter, |