[PATCH v3 01/12] Revert "KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock"

[Maxim Levitsky <mlevitsk@redhat.com>]

From: Sean Christopherson <seanjc@google.com>

This together with the next patch will fix a future race between
kvm_zap_gfn_range and the page fault handler, which will happen
when AVIC memslot is going to be only partially disabled.

This is based on a patch suggested by Sean Christopherson:
https://lkml.org/lkml/2021/7/22/1025

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/x86/kvm/mmu/mmu.c     | 19 ++++++++-----------
 arch/x86/kvm/mmu/tdp_mmu.c | 15 ++++-----------
 arch/x86/kvm/mmu/tdp_mmu.h | 11 ++++-------
 3 files changed, 16 insertions(+), 29 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index a8cdfd8d45c4..9d78cb1c0f35 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5638,8 +5638,9 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 	int i;
 	bool flush = false;
 
+	write_lock(&kvm->mmu_lock);
+
 	if (kvm_memslots_have_rmaps(kvm)) {
-		write_lock(&kvm->mmu_lock);
 		for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
 			slots = __kvm_memslots(kvm, i);
 			kvm_for_each_memslot(memslot, slots) {
@@ -5659,22 +5660,18 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 		}
 		if (flush)
 			kvm_flush_remote_tlbs_with_address(kvm, gfn_start, gfn_end);
-		write_unlock(&kvm->mmu_lock);
 	}
 
 	if (is_tdp_mmu_enabled(kvm)) {
-		flush = false;
-
-		read_lock(&kvm->mmu_lock);
 		for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
 			flush = kvm_tdp_mmu_zap_gfn_range(kvm, i, gfn_start,
-							  gfn_end, flush, true);
-		if (flush)
-			kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
-							   gfn_end);
-
-		read_unlock(&kvm->mmu_lock);
+							  gfn_end, flush);
 	}
+
+	if (flush)
+		kvm_flush_remote_tlbs_with_address(kvm, gfn_start, gfn_end);
+
+	write_unlock(&kvm->mmu_lock);
 }
 
 static bool slot_rmap_write_protect(struct kvm *kvm,
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 43f12f5d12c0..3e0222ce3f4e 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -777,21 +777,15 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
  * non-root pages mapping GFNs strictly within that range. Returns true if
  * SPTEs have been cleared and a TLB flush is needed before releasing the
  * MMU lock.
- *
- * If shared is true, this thread holds the MMU lock in read mode and must
- * account for the possibility that other threads are modifying the paging
- * structures concurrently. If shared is false, this thread should hold the
- * MMU in write mode.
  */
 bool __kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id, gfn_t start,
-				 gfn_t end, bool can_yield, bool flush,
-				 bool shared)
+				 gfn_t end, bool can_yield, bool flush)
 {
 	struct kvm_mmu_page *root;
 
-	for_each_tdp_mmu_root_yield_safe(kvm, root, as_id, shared)
+	for_each_tdp_mmu_root_yield_safe(kvm, root, as_id, false)
 		flush = zap_gfn_range(kvm, root, start, end, can_yield, flush,
-				      shared);
+				      false);
 
 	return flush;
 }
@@ -803,8 +797,7 @@ void kvm_tdp_mmu_zap_all(struct kvm *kvm)
 	int i;
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
-		flush = kvm_tdp_mmu_zap_gfn_range(kvm, i, 0, max_gfn,
-						  flush, false);
+		flush = kvm_tdp_mmu_zap_gfn_range(kvm, i, 0, max_gfn, flush);
 
 	if (flush)
 		kvm_flush_remote_tlbs(kvm);
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index b224d126adf9..358f447d4012 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -20,14 +20,11 @@ void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
 			  bool shared);
 
 bool __kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id, gfn_t start,
-				 gfn_t end, bool can_yield, bool flush,
-				 bool shared);
+				 gfn_t end, bool can_yield, bool flush);
 static inline bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id,
-					     gfn_t start, gfn_t end, bool flush,
-					     bool shared)
+					     gfn_t start, gfn_t end, bool flush)
 {
-	return __kvm_tdp_mmu_zap_gfn_range(kvm, as_id, start, end, true, flush,
-					   shared);
+	return __kvm_tdp_mmu_zap_gfn_range(kvm, as_id, start, end, true, flush);
 }
 static inline bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
 {
@@ -44,7 +41,7 @@ static inline bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
 	 */
 	lockdep_assert_held_write(&kvm->mmu_lock);
 	return __kvm_tdp_mmu_zap_gfn_range(kvm, kvm_mmu_page_as_id(sp),
-					   sp->gfn, end, false, false, false);
+					   sp->gfn, end, false, false);
 }
 
 void kvm_tdp_mmu_zap_all(struct kvm *kvm);
-- 
2.26.3