linux-kernel - Re: [PATCH v12 57/84] KVM: RISC-V: Mark "struct page" pfns accessed before dropping mmu

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Message-ID: <20240731-f034f3516f0fffede877c68d@orel>
Date: Wed, 31 Jul 2024 10:12:31 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Tianrui Zhao <zhaotianrui@...ngson.cn>, 
	Bibo Mao <maobibo@...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>, 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 57/84] KVM: RISC-V: Mark "struct page" pfns accessed
 before dropping mmu_lock

On Fri, Jul 26, 2024 at 04:52:06PM GMT, Sean Christopherson wrote:
> Mark pages accessed before dropping mmu_lock when faulting in guest memory
> so that RISC-V can convert to kvm_release_faultin_page() without tripping
> its lockdep assertion on mmu_lock being held.  Marking pages accessed
> outside of mmu_lock is ok (not great, but safe), but marking pages _dirty_
> outside of mmu_lock can make filesystems unhappy.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/riscv/kvm/mmu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index 06aa5a0d056d..806f68e70642 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -683,10 +683,10 @@ int kvm_riscv_gstage_map(struct kvm_vcpu *vcpu,
>  out_unlock:
>  	if ((!ret || ret == -EEXIST) && writable)
>  		kvm_set_pfn_dirty(hfn);
> +	else
> +		kvm_release_pfn_clean(hfn);
>  
>  	spin_unlock(&kvm->mmu_lock);
> -	kvm_set_pfn_accessed(hfn);
> -	kvm_release_pfn_clean(hfn);
>  	return ret;
>  }
>  
> -- 
> 2.46.0.rc1.232.g9752f9e123-goog
>

Reviewed-by: Andrew Jones <ajones@...tanamicro.com>