linux-kernel - Re: [PATCH v3 6/8] KVM: Fully serialize gfn=>pfn cache refresh via mutex

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Message-ID: <d84d9853-d055-50b6-669f-de2f24304f15@redhat.com>
Date:   Fri, 20 May 2022 17:24:51 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshanlai@...il.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH v3 6/8] KVM: Fully serialize gfn=>pfn cache refresh via
 mutex

On 4/29/22 23:00, Sean Christopherson wrote:
> diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
> index 05cb0bcbf662..eaef31462bbe 100644
> --- a/virt/kvm/pfncache.c
> +++ b/virt/kvm/pfncache.c
> @@ -157,6 +157,13 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
>   	if (page_offset + len > PAGE_SIZE)
>   		return -EINVAL;
>   
> +	/*
> +	 * If another task is refreshing the cache, wait for it to complete.
> +	 * There is no guarantee that concurrent refreshes will see the same
> +	 * gpa, memslots generation, etc..., so they must be fully serialized.
> +	 */
> +	mutex_lock(&gpc->refresh_lock);
> +
>   	write_lock_irq(&gpc->lock);
>   
>   	old_pfn = gpc->pfn;
> @@ -248,6 +255,8 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
>    out:
>   	write_unlock_irq(&gpc->lock);
>   
> +	mutex_unlock(&gpc->refresh_lock);
> +
>   	gpc_release_pfn_and_khva(kvm, old_pfn, old_khva);
>   
>   	return ret;

Does kvm_gfn_to_pfn_cache_unmap also need to take the mutex, to avoid 
the WARN_ON(gpc->valid)?

Paolo