linux-kernel - Re: [PATCH v4 3/7] KVM: x86/mmu: Recover TDP MMU NX huge pages using MMU read lock

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Message-ID: <20250616181144.2874709-1-jthoughton@google.com>
Date: Mon, 16 Jun 2025 18:11:44 +0000
From: James Houghton <jthoughton@...gle.com>
To: lkp@...el.com, pbonzini@...hat.com, seanjc@...gle.com
Cc: dmatlack@...gle.com, jthoughton@...gle.com, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
	oe-kbuild-all@...ts.linux.dev, vipinsh@...gle.com
Subject: Re: [PATCH v4 3/7] KVM: x86/mmu: Recover TDP MMU NX huge pages using
 MMU read lock

> All errors (new ones prefixed by >>):
> 
>    arch/x86/kvm/mmu/mmu.c:7570:28: error: use of undeclared identifier 'KVM_TDP_MMU'
>     7570 |         bool is_tdp = mmu_type == KVM_TDP_MMU;
>          |                                   ^
> >> arch/x86/kvm/mmu/mmu.c:7594:25: error: no member named 'tdp_mmu_pages_lock' in 'struct kvm_arch'
>     7594 |                         spin_lock(&kvm->arch.tdp_mmu_pages_lock);
>          |                                    ~~~~~~~~~ ^
>    arch/x86/kvm/mmu/mmu.c:7597:28: error: no member named 'tdp_mmu_pages_lock' in 'struct kvm_arch'
>     7597 |                                 spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
>          |                                              ~~~~~~~~~ ^
>    arch/x86/kvm/mmu/mmu.c:7617:27: error: no member named 'tdp_mmu_pages_lock' in 'struct kvm_arch'
>     7617 |                         spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
>          |                                      ~~~~~~~~~ ^
>    4 errors generated.

Fixup for this below.

I also realized that the variable name `is_tdp` is bad/misleading, so I've
changed it to `is_tdp_mmu` as part of this fixup too. Sean/Paolo, let me know
if I should just go ahead and post the fixed series, given the size of this
fixup.

I don't really like having to #ifdef all the places where we take
tdp_mmu_pages_lock, but I couldn't find a way to avoid that. Even doing

  #ifndef CONFIG_X86_64
  #define is_tdp_mmu false
  #endif

didn't work. :(

Anyway, here's the fixup:

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 10ba328b664d7..7df1b4ead705b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7564,10 +7564,10 @@ static bool kvm_mmu_sp_dirty_logging_enabled(struct kvm *kvm,
 }
 
 static void kvm_recover_nx_huge_pages(struct kvm *kvm,
-				      enum kvm_mmu_type mmu_type)
+				      const enum kvm_mmu_type mmu_type)
 {
 	unsigned long to_zap = nx_huge_pages_to_zap(kvm, mmu_type);
-	bool is_tdp = mmu_type == KVM_TDP_MMU;
+	bool is_tdp_mmu = mmu_type == KVM_TDP_MMU;
 	struct list_head *nx_huge_pages;
 	struct kvm_mmu_page *sp;
 	LIST_HEAD(invalid_list);
@@ -7577,7 +7577,7 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm,
 	nx_huge_pages = &kvm->arch.possible_nx_huge_pages[mmu_type].pages;
 
 	rcu_idx = srcu_read_lock(&kvm->srcu);
-	if (is_tdp)
+	if (is_tdp_mmu)
 		read_lock(&kvm->mmu_lock);
 	else
 		write_lock(&kvm->mmu_lock);
@@ -7590,11 +7590,15 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm,
 	rcu_read_lock();
 
 	for ( ; to_zap; --to_zap) {
-		if (is_tdp)
+#ifdef CONFIG_X86_64
+		if (is_tdp_mmu)
 			spin_lock(&kvm->arch.tdp_mmu_pages_lock);
+#endif
 		if (list_empty(nx_huge_pages)) {
-			if (is_tdp)
+#ifdef CONFIG_X86_64
+			if (is_tdp_mmu)
 				spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
+#endif
 			break;
 		}
 
@@ -7613,8 +7617,10 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm,
 
 		unaccount_nx_huge_page(kvm, sp);
 
-		if (is_tdp)
+#ifdef CONFIG_X86_64
+		if (is_tdp_mmu)
 			spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
+#endif
 
 		/*
 		 * Do not attempt to recover any NX Huge Pages that are being
@@ -7624,7 +7630,7 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm,
 		 * logging is disabled.
 		 */
 		if (!kvm_mmu_sp_dirty_logging_enabled(kvm, sp)) {
-			if (is_tdp)
+			if (is_tdp_mmu)
 				flush |= kvm_tdp_mmu_zap_possible_nx_huge_page(kvm, sp);
 			else
 				kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list);
@@ -7637,7 +7643,7 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm,
 			kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, flush);
 			rcu_read_unlock();
 
-			if (is_tdp)
+			if (is_tdp_mmu)
 				cond_resched_rwlock_read(&kvm->mmu_lock);
 			else
 				cond_resched_rwlock_write(&kvm->mmu_lock);
@@ -7650,7 +7656,7 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm,
 
 	rcu_read_unlock();
 
-	if (is_tdp)
+	if (is_tdp_mmu)
 		read_unlock(&kvm->mmu_lock);
 	else
 		write_unlock(&kvm->mmu_lock);