linux-kernel - Re: [PATCH v12 65/84] KVM: LoongArch: Mark "struct page" pfns accessed only in "slow" page fault path

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Message-ID: <d5405245-edd3-9bc5-0c40-282a30e46fae@loongson.cn>
Date: Fri, 2 Aug 2024 15:34:38 +0800
From: maobibo <maobibo@...ngson.cn>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oliver.upton@...ux.dev>, Tianrui Zhao
 <zhaotianrui@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
 Michael Ellerman <mpe@...erman.id.au>, Anup Patel <anup@...infault.org>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc: kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 kvmarm@...ts.linux.dev, loongarch@...ts.linux.dev,
 linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org, David Matlack <dmatlack@...gle.com>,
 David Stevens <stevensd@...omium.org>
Subject: Re: [PATCH v12 65/84] KVM: LoongArch: Mark "struct page" pfns
 accessed only in "slow" page fault path



On 2024/7/27 上午7:52, Sean Christopherson wrote:
> Mark pages accessed only in the slow path, before dropping mmu_lock when
> faulting in guest memory so that LoongArch can convert to
> kvm_release_faultin_page() without tripping its lockdep assertion on
> mmu_lock being held.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/loongarch/kvm/mmu.c | 20 ++------------------
>   1 file changed, 2 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/loongarch/kvm/mmu.c b/arch/loongarch/kvm/mmu.c
> index 364dd35e0557..52b5c16cf250 100644
> --- a/arch/loongarch/kvm/mmu.c
> +++ b/arch/loongarch/kvm/mmu.c
> @@ -552,12 +552,10 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
>   static int kvm_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa, bool write)
>   {
>   	int ret = 0;
> -	kvm_pfn_t pfn = 0;
>   	kvm_pte_t *ptep, changed, new;
>   	gfn_t gfn = gpa >> PAGE_SHIFT;
>   	struct kvm *kvm = vcpu->kvm;
>   	struct kvm_memory_slot *slot;
> -	struct page *page;
>   
>   	spin_lock(&kvm->mmu_lock);
>   
> @@ -570,8 +568,6 @@ static int kvm_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa, bool writ
>   
>   	/* Track access to pages marked old */
>   	new = kvm_pte_mkyoung(*ptep);
> -	/* call kvm_set_pfn_accessed() after unlock */
> -
>   	if (write && !kvm_pte_dirty(new)) {
>   		if (!kvm_pte_write(new)) {
>   			ret = -EFAULT;
> @@ -595,23 +591,11 @@ static int kvm_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa, bool writ
>   	}
>   
>   	changed = new ^ (*ptep);
> -	if (changed) {
> +	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);
>   
> -	if (changed) {
> -		if (kvm_pte_young(changed))
> -			kvm_set_pfn_accessed(pfn);
> -
> -		if (page)
> -			put_page(page);
> -	}
> -
>   	if (kvm_pte_dirty(changed))
>   		mark_page_dirty(kvm, gfn);
>   
> 
Reviewed-by: Bibo Mao <maobibo@...ngson.cn>