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-rw-r--r--arch/x86/kvm/mmu/mmu.c20
-rw-r--r--arch/x86/kvm/mmu/tdp_mmu.c75
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;
}