kvm: x86/mmu: Support disabling dirty logging for the tdp MMU

Dirty logging ultimately breaks down MMU mappings to 4k granularity.
When dirty logging is no longer needed, these granaular mappings
represent a useless performance penalty. When dirty logging is disabled,
search the paging structure for mappings that could be re-constituted
into a large page mapping. Zap those mappings so that they can be
faulted in again at a higher mapping level.

Tested by running kvm-unit-tests and KVM selftests on an Intel Haswell
machine. This series introduced no new failures.

This series can be viewed in Gerrit at:
	https://linux-review.googlesource.com/c/virt/kvm/kvm/+/2538

Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20201014182700.2888246-17-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 0c64643..cd1be20 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5544,6 +5544,9 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
        spin_lock(&kvm->mmu_lock);
        slot_handle_leaf(kvm, (struct kvm_memory_slot *)memslot,
                         kvm_mmu_zap_collapsible_spte, true);
+
+       if (kvm->arch.tdp_mmu_enabled)
+               kvm_tdp_mmu_zap_collapsible_sptes(kvm, memslot);
        spin_unlock(&kvm->mmu_lock);
 }
 

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 7181b4a..0f181f3 100644 (file)
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1020,3 +1020,61 @@ bool kvm_tdp_mmu_slot_set_dirty(struct kvm *kvm, struct kvm_memory_slot *slot)
        return spte_set;
 }
 
+/*
+ * Clear non-leaf entries (and free associated page tables) which could
+ * be replaced by large mappings, for GFNs within the slot.
+ */
+static void zap_collapsible_spte_range(struct kvm *kvm,
+                                      struct kvm_mmu_page *root,
+                                      gfn_t start, gfn_t end)
+{
+       struct tdp_iter iter;
+       kvm_pfn_t pfn;
+       bool spte_set = false;
+
+       tdp_root_for_each_pte(iter, root, start, end) {
+               if (!is_shadow_present_pte(iter.old_spte) ||
+                   is_last_spte(iter.old_spte, iter.level))
+                       continue;
+
+               pfn = spte_to_pfn(iter.old_spte);
+               if (kvm_is_reserved_pfn(pfn) ||
+                   !PageTransCompoundMap(pfn_to_page(pfn)))
+                       continue;
+
+               tdp_mmu_set_spte(kvm, &iter, 0);
+
+               spte_set = tdp_mmu_iter_flush_cond_resched(kvm, &iter);
+       }
+
+       if (spte_set)
+               kvm_flush_remote_tlbs(kvm);
+}
+
+/*
+ * Clear non-leaf entries (and free associated page tables) which could
+ * be replaced by large mappings, for GFNs within the slot.
+ */
+void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
+                                      const struct kvm_memory_slot *slot)
+{
+       struct kvm_mmu_page *root;
+       int root_as_id;
+
+       for_each_tdp_mmu_root(kvm, root) {
+               root_as_id = kvm_mmu_page_as_id(root);
+               if (root_as_id != slot->as_id)
+                       continue;
+
+               /*
+                * Take a reference on the root so that it cannot be freed if
+                * this thread releases the MMU lock and yields in this loop.
+                */
+               kvm_mmu_get_root(kvm, root);
+
+               zap_collapsible_spte_range(kvm, root, slot->base_gfn,
+                                          slot->base_gfn + slot->npages);
+
+               kvm_mmu_put_root(kvm, root);
+       }
+}

diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index ece66f1..8cc902b 100644 (file)
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -38,4 +38,6 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
                                       gfn_t gfn, unsigned long mask,
                                       bool wrprot);
 bool kvm_tdp_mmu_slot_set_dirty(struct kvm *kvm, struct kvm_memory_slot *slot);
+void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
+                                      const struct kvm_memory_slot *slot);
 #endif /* __KVM_X86_MMU_TDP_MMU_H */