diff options
| -rw-r--r-- | arch/x86/kvm/mmu/mmu.c | 20 | ||||
| -rw-r--r-- | arch/x86/kvm/mmu/tdp_mmu.c | 75 |
2 files changed, 66 insertions, 29 deletions
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index c39674d19260..99f7b2f3d82a 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -831,6 +831,15 @@ static void account_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp) gfn_t gfn; kvm->arch.indirect_shadow_pages++; + /* + * Ensure indirect_shadow_pages is elevated prior to re-reading guest + * child PTEs in FNAME(gpte_changed), i.e. guarantee either in-flight + * emulated writes are visible before re-reading guest PTEs, or that + * an emulated write will see the elevated count and acquire mmu_lock + * to update SPTEs. Pairs with the smp_mb() in kvm_mmu_track_write(). + */ + smp_mb(); + gfn = sp->gfn; slots = kvm_memslots_for_spte_role(kvm, sp->role); slot = __gfn_to_memslot(slots, gfn); @@ -5787,10 +5796,15 @@ void kvm_mmu_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new, bool flush = false; /* - * If we don't have indirect shadow pages, it means no page is - * write-protected, so we can exit simply. + * When emulating guest writes, ensure the written value is visible to + * any task that is handling page faults before checking whether or not + * KVM is shadowing a guest PTE. This ensures either KVM will create + * the correct SPTE in the page fault handler, or this task will see + * a non-zero indirect_shadow_pages. Pairs with the smp_mb() in + * account_shadowed(). */ - if (!READ_ONCE(vcpu->kvm->arch.indirect_shadow_pages)) + smp_mb(); + if (!vcpu->kvm->arch.indirect_shadow_pages) return; write_lock(&vcpu->kvm->mmu_lock); diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index b5be7e949bd8..1259dd63defc 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -530,6 +530,31 @@ static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn, kvm_set_pfn_accessed(spte_to_pfn(old_spte)); } +static inline int __tdp_mmu_set_spte_atomic(struct tdp_iter *iter, u64 new_spte) +{ + u64 *sptep = rcu_dereference(iter->sptep); + + /* + * The caller is responsible for ensuring the old SPTE is not a REMOVED + * SPTE. KVM should never attempt to zap or manipulate a REMOVED SPTE, + * and pre-checking before inserting a new SPTE is advantageous as it + * avoids unnecessary work. + */ + WARN_ON_ONCE(iter->yielded || is_removed_spte(iter->old_spte)); + + /* + * Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and + * does not hold the mmu_lock. On failure, i.e. if a different logical + * CPU modified the SPTE, try_cmpxchg64() updates iter->old_spte with + * the current value, so the caller operates on fresh data, e.g. if it + * retries tdp_mmu_set_spte_atomic() + */ + if (!try_cmpxchg64(sptep, &iter->old_spte, new_spte)) + return -EBUSY; + + return 0; +} + /* * tdp_mmu_set_spte_atomic - Set a TDP MMU SPTE atomically * and handle the associated bookkeeping. Do not mark the page dirty @@ -551,27 +576,13 @@ static inline int tdp_mmu_set_spte_atomic(struct kvm *kvm, struct tdp_iter *iter, u64 new_spte) { - u64 *sptep = rcu_dereference(iter->sptep); - - /* - * The caller is responsible for ensuring the old SPTE is not a REMOVED - * SPTE. KVM should never attempt to zap or manipulate a REMOVED SPTE, - * and pre-checking before inserting a new SPTE is advantageous as it - * avoids unnecessary work. - */ - WARN_ON_ONCE(iter->yielded || is_removed_spte(iter->old_spte)); + int ret; lockdep_assert_held_read(&kvm->mmu_lock); - /* - * Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and - * does not hold the mmu_lock. On failure, i.e. if a different logical - * CPU modified the SPTE, try_cmpxchg64() updates iter->old_spte with - * the current value, so the caller operates on fresh data, e.g. if it - * retries tdp_mmu_set_spte_atomic() - */ - if (!try_cmpxchg64(sptep, &iter->old_spte, new_spte)) - return -EBUSY; + ret = __tdp_mmu_set_spte_atomic(iter, new_spte); + if (ret) + return ret; handle_changed_spte(kvm, iter->as_id, iter->gfn, iter->old_spte, new_spte, iter->level, true); @@ -584,13 +595,17 @@ static inline int tdp_mmu_zap_spte_atomic(struct kvm *kvm, { int ret; + lockdep_assert_held_read(&kvm->mmu_lock); + /* - * Freeze the SPTE by setting it to a special, - * non-present value. This will stop other threads from - * immediately installing a present entry in its place - * before the TLBs are flushed. + * Freeze the SPTE by setting it to a special, non-present value. This + * will stop other threads from immediately installing a present entry + * in its place before the TLBs are flushed. + * + * Delay processing of the zapped SPTE until after TLBs are flushed and + * the REMOVED_SPTE is replaced (see below). */ - ret = tdp_mmu_set_spte_atomic(kvm, iter, REMOVED_SPTE); + ret = __tdp_mmu_set_spte_atomic(iter, REMOVED_SPTE); if (ret) return ret; @@ -599,12 +614,20 @@ static inline int tdp_mmu_zap_spte_atomic(struct kvm *kvm, /* * 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. + * overwrite the special removed SPTE value. Use the raw write helper to + * avoid an unnecessary check on volatile bits. */ __kvm_tdp_mmu_write_spte(iter->sptep, SHADOW_NONPRESENT_VALUE); + /* + * Process the zapped SPTE after flushing TLBs, and after replacing + * REMOVED_SPTE with 0. This minimizes the amount of time vCPUs are + * blocked by the REMOVED_SPTE and reduces contention on the child + * SPTEs. + */ + handle_changed_spte(kvm, iter->as_id, iter->gfn, iter->old_spte, + 0, iter->level, true); + return 0; } |