linux-kernel - [PATCH] LoongArch: KVM: Mark page accessed and dirty with mmu

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Message-Id: <20240611034609.3442344-1-maobibo@loongson.cn>
Date: Tue, 11 Jun 2024 11:46:09 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Tianrui Zhao <zhaotianrui@...ngson.cn>,
	Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>,
	kvm@...r.kernel.org,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH] LoongArch: KVM: Mark page accessed and dirty with mmu_lock

Function kvm_set_pfn_accessed() is somewhat complicated, originally
we want to reduce coverity range of mmu_lock, so move function
kvm_set_pfn_accessed() and kvm_set_pfn_dirty() out of mmu_lock.

However with migration test where vm has some workload, there is no
response when VM finishes migration. When mmu_lock is released, pfn page
may be replaced with other pages, it is unreasonable to set old replaced
pfn page with accessed or dirty.

Here move function kvm_set_pfn_accessed() and kvm_set_pfn_dirty() with
mmu_lock held, VM works after many times of migrations.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 arch/loongarch/kvm/mmu.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/arch/loongarch/kvm/mmu.c b/arch/loongarch/kvm/mmu.c
index ec8c43aad724..91998e95db87 100644
--- a/arch/loongarch/kvm/mmu.c
+++ b/arch/loongarch/kvm/mmu.c
@@ -591,21 +591,14 @@ 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);
-	}
-	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 (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);
+		}
 	}
-	return ret;
 out:
 	spin_unlock(&kvm->mmu_lock);
 	return ret;

base-commit: 2df0193e62cf887f373995fb8a91068562784adc
-- 
2.39.3