linux-kernel - [PATCH v3 6/7] LoongArch: KVM: Mark page accessed and dirty with page ref added

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Message-Id: <20240624071422.3473789-7-maobibo@loongson.cn>
Date: Mon, 24 Jun 2024 15:14:21 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Tianrui Zhao <zhaotianrui@...ngson.cn>,
	Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>,
	Sean Christopherson <seanjc@...gle.com>,
	kvm@...r.kernel.org,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	WANG Rui <wangrui@...ngson.cn>
Subject: [PATCH v3 6/7] LoongArch: KVM: Mark page accessed and dirty with page ref added

Function kvm_map_page_fast() is fast path of secondary mmu page fault
flow, pfn is parsed from secondary mmu page table walker. However
the corresponding page reference is not added, it is dangerious to
access page out of mmu_lock.

Here page ref is added inside mmu_lock, function kvm_set_pfn_accessed()
and kvm_set_pfn_dirty() is called with page ref added, so that the
page will not be freed by others.

Also kvm_set_pfn_accessed() is removed here since it is called in
the following function kvm_release_pfn_clean().

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 arch/loongarch/kvm/mmu.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/arch/loongarch/kvm/mmu.c b/arch/loongarch/kvm/mmu.c
index 10da8a63cd3d..7f744e6679a8 100644
--- a/arch/loongarch/kvm/mmu.c
+++ b/arch/loongarch/kvm/mmu.c
@@ -557,6 +557,7 @@ static int kvm_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa, bool writ
 	gfn_t gfn = gpa >> PAGE_SHIFT;
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_memory_slot *slot;
+	struct page *page;
 
 	spin_lock(&kvm->mmu_lock);
 
@@ -599,19 +600,22 @@ static int kvm_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa, bool writ
 	if (changed) {
 		kvm_set_pte(ptep, new);
 		pfn = kvm_pte_pfn(new);
+		page = kvm_pfn_to_refcounted_page(pfn);
+		if (page)
+			get_page(page);
 	}
 	spin_unlock(&kvm->mmu_lock);
 
-	/*
-	 * Fixme: pfn may be freed after mmu_lock
-	 * kvm_try_get_pfn(pfn)/kvm_release_pfn pair to prevent this?
-	 */
-	if (kvm_pte_young(changed))
-		kvm_set_pfn_accessed(pfn);
+	if (changed) {
+		if (kvm_pte_young(changed))
+			kvm_set_pfn_accessed(pfn);
 
-	if (kvm_pte_dirty(changed)) {
-		mark_page_dirty(kvm, gfn);
-		kvm_set_pfn_dirty(pfn);
+		if (kvm_pte_dirty(changed)) {
+			mark_page_dirty(kvm, gfn);
+			kvm_set_pfn_dirty(pfn);
+		}
+		if (page)
+			put_page(page);
 	}
 	return ret;
 out:
@@ -920,7 +924,6 @@ static int kvm_map_page(struct kvm_vcpu *vcpu, unsigned long gpa, bool write)
 		kvm_set_pfn_dirty(pfn);
 	}
 
-	kvm_set_pfn_accessed(pfn);
 	kvm_release_pfn_clean(pfn);
 out:
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
-- 
2.39.3