[PATCH v2 25/28] KVM: x86/mmu: Obsolete all roots if memattr contains gPTEs

[Paolo Bonzini]

Note that the zapping of obsolete roots needs to happen after
mmu_lock is dropped, so introduce a separate kvm_arch callback.
The two map neatly to the "front" and "back" halves of
kvm_mmu_zap_all_fast().

Co-developed-by: Nicolas Saenz Julienne <nsaenz@xxxxxxxxxx>
Signed-off-by: Nicolas Saenz Julienne <nsaenz@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c   | 32 ++++++++++++++++++++++++++++++++
 include/linux/kvm_host.h |  1 +
 virt/kvm/kvm_main.c      |  7 +++++--
 3 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 097095f71d60..d658cfe31cd9 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -8265,6 +8265,7 @@ bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
 {
 	unsigned long attrs = range->arg.attributes;
 	struct kvm_memory_slot *slot = range->slot;
+	struct kvm_mmu_page *sp;
 	int level;
 
 	lockdep_assert_held_write(&kvm->mmu_lock);
@@ -8320,9 +8321,40 @@ bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
 				hugepage_set_mixed(slot, gfn, level);
 		}
 	}
+
+	/*
+	 * There are special considerations when applying an memory protection
+	 * attibute against a GPTE page. If set read-only, access/dirty bits
+	 * within that page shouldn't be updated. If set non-accesible,
+	 * accessing a virtual address that requires traversing that GPTE page
+	 * should fault.
+	 *
+	 * On TDP enabled guests, the CPU faults on the GPTE address upon
+	 * detecting such a situation.
+	 *
+	 * On non-TDP, upon detecting this situation, and based on the fact it
+	 * should be a rare occasion, invalidate all the mmu roots.
+	 */
+	for (gfn_t gfn = range->start; gfn < range->end; gfn++) {
+		for_each_gfn_valid_sp_with_gptes(kvm, sp, gfn) {
+			__kvm_mmu_zap_all_fast_front_half(kvm);
+			return false;
+		}
+	}
 	return false;
 }
 
+void kvm_arch_post_set_memory_attributes_unlocked(struct kvm *kvm)
+{
+	/*
+	 * This may also be called if no zap was done in
+	 * kvm_arch_post_set_memory_attributes().  It is not an issue because
+	 * __kvm_mmu_zap_all_fast_back_half() is cheap when it does not do
+	 * anything.
+	 */
+	 __kvm_mmu_zap_all_fast_back_half(kvm);
+}
+
 void kvm_mmu_init_memslot_memory_attributes(struct kvm *kvm,
 					    struct kvm_memory_slot *slot)
 {
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e9c0932f150e..33f3199a855f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2624,6 +2624,7 @@ bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm,
 					struct kvm_gfn_range *range);
 bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
 					 struct kvm_gfn_range *range);
+void kvm_arch_post_set_memory_attributes_unlocked(struct kvm *kvm);
 bool kvm_mem_attributes_valid(struct kvm *kvm, unsigned long attrs);
 u64 kvm_supported_mem_attributes(struct kvm *kvm);
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 24f46dce192e..ccbec4796e4b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2516,7 +2516,7 @@ static bool kvm_range_memory_attributes_need_sync(struct kvm *kvm,
 	return kvm_range_has_any_memory_attributes(kvm, start, end, mask);
 }
 
-static __always_inline void kvm_handle_gfn_range(struct kvm *kvm,
+static __always_inline bool kvm_handle_gfn_range(struct kvm *kvm,
 						 struct kvm_mmu_notifier_range *range)
 {
 	struct kvm_gfn_range gfn_range;
@@ -2566,6 +2566,8 @@ static __always_inline void kvm_handle_gfn_range(struct kvm *kvm,
 
 	if (found_memslot)
 		KVM_MMU_UNLOCK(kvm);
+
+	return found_memslot;
 }
 
 static bool kvm_pre_set_memory_attributes(struct kvm *kvm,
@@ -2652,7 +2654,8 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
 	smp_store_release(&kvm->mem_attrs.generation,
 			  kvm->mem_attrs.generation + 1);
 
-	kvm_handle_gfn_range(kvm, &post_set_range);
+	if (kvm_handle_gfn_range(kvm, &post_set_range))
+		kvm_arch_post_set_memory_attributes_unlocked(kvm);
 
 out_unlock:
 	mutex_unlock(&kvm->slots_lock);
-- 
2.52.0